diff --git a/@dash/checkStrsInList.m b/@dash/checkStrsInList.m
index 5f570b65..e5f20c77 100644
--- a/@dash/checkStrsInList.m
+++ b/@dash/checkStrsInList.m
@@ -27,9 +27,9 @@
     % Informative error message
     badName = name;
     if numel(input)>1
-        badName = sprintf('Element %.f in %s (%s)', bad, name, input(bad));
+        badName = sprintf('Element %.f in %s', bad, name);
     end
-    error('%s is not a %s. Allowed values are %s.', badName, listName, dash.messageList(list));
+    error('%s (%s) is not a %s. Allowed values are %s.', badName, input(bad), listName, dash.messageList(list));
 end
 
 end
\ No newline at end of file
diff --git a/@ensemble/ensemble.m b/@ensemble/ensemble.m
index 66e491e8..5d6471c6 100644
--- a/@ensemble/ensemble.m
+++ b/@ensemble/ensemble.m
@@ -15,8 +15,9 @@
     
     properties (SetAccess = private)
         file; % The .ens file associated with the object
+        name; % The name of the ensemble object
         
-        hasnan; % Whether a variable has NaN in an ensemble member
+        has_nan; % Whether a variable has NaN in an ensemble member
         metadata; % Ensemble metadata object for the saved state vector ensemble
         stateVector; % The stateVector object used to build the ensemble
         
@@ -26,7 +27,7 @@
     
     % Constructor
     methods
-        function obj = ensemble(filename)
+        function obj = ensemble(filename, name)
             %% Creates a new ensemble object
             %
             % obj = ensemble(filename)
@@ -37,12 +38,17 @@
             % Returns an ensemble object for a .ens file with the specified
             % full file path.
             %
+            % obj = ensemble(filename, name)
+            % Provides an identifying name for the ensemble object.
+            %
             % ----- Inputs -----
             %
             % filename: The name of a .ens file on the active path. A string.
             %
             % fullname: The full file path to a .ens file. A string.
             %
+            % name: An identifying name for the ensemble object. A string.
+            %
             % ----- Outputs -----
             %
             % obj: An ensemble object for the specified .ens file.
@@ -55,6 +61,12 @@
             % Members and variables are unspecified.
             obj.members = [];
             obj.variables = [];
+
+            % Update name (error checking via ensembleMetadata)
+            if exist('name','var')
+                obj.metadata = obj.metadata.rename(name);
+                obj.name = name;
+            end
         end
     end
         
@@ -75,5 +87,7 @@
         obj = useVariables(obj, variables);
         varNames = variableNames(obj);
         s = info(obj);
+        nanMembers = hasnan(obj, varNames);
+        obj = rename(obj, newName);
     end
 end
\ No newline at end of file
diff --git a/@ensemble/hasnan.m b/@ensemble/hasnan.m
new file mode 100644
index 00000000..7ce2cd39
--- /dev/null
+++ b/@ensemble/hasnan.m
@@ -0,0 +1,46 @@
+function[nanMembers] = hasnan(obj, varNames)
+%% Indicates whether ensemble members contain NaN elements for variables
+% in a state vector ensemble.
+%
+% nanMembers = obj.hasnan
+% Returns a row vector that indicates which ensemble members contain NaN
+% elements.
+%
+% nanVars = obj.hasnan(varNames)
+% Returns a logical matrix that indicates whether specified variables have
+% NaN elements in ensemble members.
+%
+% nanVars = obj.hasnan([])
+% Indicates whether variables have NaN elements in ensemble members for
+% each variable in a state vector.
+%
+% ----- Inputs -----
+%
+% varNames: A list of variables in a state vector. A string vector or
+%    cellstring vector.
+%
+% ----- Outputs -----
+%
+% nanMembers: A logical row vector with one element per ensemble member. True
+%    elements indicate that the ensemble member contains NaN elements.
+%
+% nanVars: A logical matrix with one column per ensemble member. Each row
+%    indicates whether a particular variable has NaN elements in each
+%    ensemble member.
+
+% If no inputs, return summary for all variables
+if ~exist('varNames','var')
+    nanMembers = any(obj.has_nan,1);
+    return;
+end
+
+% Otherwise, return for specified variables
+allVars = obj.metadata.variableNames;
+if isempty(varNames)
+    v = 1:numel(allVars);
+else
+    v = dash.checkStrsInList(varNames, allVars, 'varNames', 'variable in the state vector');
+end
+nanMembers = obj.has_nan(v,:);
+
+end    
\ No newline at end of file
diff --git a/@ensemble/rename.m b/@ensemble/rename.m
new file mode 100644
index 00000000..6a91d9a0
--- /dev/null
+++ b/@ensemble/rename.m
@@ -0,0 +1,18 @@
+function[obj] = rename(obj, newName)
+%% Renames an ensemble object
+%
+% obj = obj.rename(newName)
+%
+% ----- Inputs -----
+%
+% newName: The new name for the ensemble object. A string.
+%
+% ----- Outputs -----
+%
+% obj: The updated ensemble object
+
+% Update name (error checking via ensembleMetadata)
+obj.metadata = obj.metadata.rename(name);
+obj.name = dash.assertStrFlag(newName, 'newName');
+
+end
\ No newline at end of file
diff --git a/@ensemble/update.m b/@ensemble/update.m
index 3543c6b9..dee9da49 100644
--- a/@ensemble/update.m
+++ b/@ensemble/update.m
@@ -13,6 +13,7 @@
 
 % If no matfile object is provided, load data into a structure
 fields = ["hasnan","metadata","stateVector"];
+props = ["has_nan", "metadata", "stateVector"];
 if ~exist('ens','var') || isempty(ens)
     ens = dash.loadMatfileFields(obj.file, fields, '.ens');
 end
@@ -20,7 +21,8 @@
 % Fill in the fields
 for f = 1:numel(fields)
     name = char(fields(f));
-    obj.(name) = ens.(name);
+    propName = char(props(f));
+    obj.(propName) = ens.(name);
 end
 
 end
\ No newline at end of file
diff --git a/@ensemble/useMembers.m b/@ensemble/useMembers.m
index de5d8ae9..df6569a9 100644
--- a/@ensemble/useMembers.m
+++ b/@ensemble/useMembers.m
@@ -19,8 +19,13 @@
 
 % Update. Error check the ensemble members. Save
 obj = obj.update;
-[~, nEns] = obj.metadata.sizes;
-members = dash.checkIndices(members, 'members', nEns, 'the number of ensemble members');
-obj.members = members(:);
+if ~exist('members','var') || isempty(members)
+    members = [];
+else
+    [~, nEns] = obj.metadata.sizes;
+    members = dash.checkIndices(members, 'members', nEns, 'the number of ensemble members');
+    members = members(:);
+end
+obj.members = members;
 
 end
\ No newline at end of file
diff --git a/@ensemble/useVariables.m b/@ensemble/useVariables.m
index 1c57fdde..efafcfb3 100644
--- a/@ensemble/useVariables.m
+++ b/@ensemble/useVariables.m
@@ -18,8 +18,13 @@
 
 % Check variables. Update. Save
 obj = obj.update;
-obj.stateVector.checkVariables(varNames);
-varNames = string(varNames);
-obj.variables = unique(varNames(:));
+if ~exist('varNames','var') || isempty(varNames)
+    varNames = [];
+else
+    obj.stateVector.checkVariables(varNames);
+    varNames = string(varNames);
+    varNames = unique(varNames(:));
+end
+obj.variables = varNames;
 
 end
\ No newline at end of file
diff --git a/@ensembleMetadata/ensembleMetadata.m b/@ensembleMetadata/ensembleMetadata.m
index 4ceaa04d..e4a58166 100644
--- a/@ensembleMetadata/ensembleMetadata.m
+++ b/@ensembleMetadata/ensembleMetadata.m
@@ -26,7 +26,7 @@
     % Jonathan King, University of Arizona, 2019-2020
     
     properties (SetAccess = private)
-        ensembleName; % Name of the ensemble
+        name; % Name of the ensemble
         vectorName; % Name of the state vector template
         
         variableNames; % Names of each metadata
@@ -51,19 +51,24 @@
     
     % Constructor
     methods
-        function obj = ensembleMetadata(sv)
-            %% Returns an ensembleMetadata object for a stateVector, ensemble, or .ens file.
+        function obj = ensembleMetadata(sv, name)
+            %% Returns an ensembleMetadata object for a stateVector.
             %
             % obj = ensembleMetadata(sv)
             % Creates an ensembleMetadata object for a state vector.
             %
+            % obj = ensembleMetadata(sv, name)
+            % Optionally gives an identifying name for the ensemble.
+            %
             % ----- Inputs -----
             %
             % sv: A stateVector object
             %
+            % name: An identifying name for the ensemble. A string
+            %
             % ----- Outputs -----
             %
-            % meta: The ensemble metadata object
+            % obj: The ensemble metadata object
 
             % Error check.
             if ~isa(sv, 'stateVector') || ~isscalar(sv)
@@ -71,7 +76,11 @@
             end
             
             % Get names and size
-            obj.ensembleName = [];
+            if exist('name','var')
+                obj.name = dash.assertStrFlag(name, 'name');
+            else
+                obj.name = [];
+            end
             obj.vectorName = sv.name;
 
             obj.nEns = 0;
@@ -151,6 +160,8 @@
     % User methods
     methods
         % variableNames -- Just a direct call to the field
+        obj = rename(obj, newName);
+
         [V, meta] = regrid(obj, X, varName, dimOrder, d, keepSingletons);
         meta = variable(obj, varName, dims, type, indices);
         meta = dimension(obj, dim, alwaysStruct);
@@ -166,5 +177,5 @@
         obj = appendMembers(obj, meta2);
         obj = extractMembers(obj, members);
     end
-    
+
 end
\ No newline at end of file
diff --git a/@ensembleMetadata/rename.m b/@ensembleMetadata/rename.m
new file mode 100644
index 00000000..127929f4
--- /dev/null
+++ b/@ensembleMetadata/rename.m
@@ -0,0 +1,16 @@
+function[obj] = rename(obj, newName)
+%% Changes the identifying ensemble name for the ensembleMetadata object.
+%
+% obj = obj.rename(newName)
+%
+% ----- Inputs -----
+%
+% newName: The new identifying name for the ensemble. A string.
+%
+% ----- Outputs -----
+%
+% obj: The updated ensembleMetadata object.
+
+obj.name = dash.assertStrFlag(newName, 'newName');
+
+end
\ No newline at end of file
diff --git a/@gridfile/add.m b/@gridfile/add.m
index 9805cce9..ded46439 100644
--- a/@gridfile/add.m
+++ b/@gridfile/add.m
@@ -1,11 +1,14 @@
 function[] = add( obj, type, file, var, dims, meta, varargin )
 % Adds a data source to a .grid file.
 %
-% obj.add( type, file, var, dims, meta )
-% Add a data source. Notes the type of data source (NetCDF vs .mat), the
-% name of the file, the name of the data variable in the file, the order of
-% the dimensions for the variable, and the metadata associated with each
-% dimension.
+% obj.add('nc', file, var, dims, meta)
+% Adds a NetCDF data source.
+%
+% obj.add('mat', file, var, dims, meta)
+% Adds a .mat data source.
+%
+% obj.add('opendap', url, var, dims, meta)
+% Adds an OPeNDAP data source.
 %
 % obj.add( ..., 'fill', fill )
 % Specifies a fill value for the data source. When data is loaded from the
@@ -38,6 +41,8 @@
 %    path. Use the full file path to add a file off the active path. All
 %    file names must include the file extension.
 %
+% url: An OPeNDAP url. A string.
+%
 % var: The name of the variable in the source file.
 %
 % dims: The order of the dimensions of the variable in the source file. A
@@ -66,7 +71,8 @@
 %
 % absolute: A scalar logical indicating whether to save data source file
 %    names as an absolute path (true), or as a path relative to the .grid
-%    file (false). Default is false.
+%    file (false). Default is false. Files located on a different drive or
+%    via an OPeNDAP url will use an absolute path.
 
 % Update the gridfile object in case the file was changed.
 obj.update;
@@ -131,13 +137,13 @@
     % The source metadata must exactly match a sequence of .grid metadata
     [inGrid, order] = ismember(value, obj.meta.(metaDims(d)), 'rows');
     if any(~inGrid)
-        error('The %s metadata in row %.f of data source %s does not match any %s metadata in .grid file %s.', metaDims(d), find(~inGrid,1), source.file, metaDims(d), obj.file);
+        error('The %s metadata in row %.f of data source %s does not match any %s metadata in .grid file %s.', metaDims(d), find(~inGrid,1), source.source, metaDims(d), obj.file);
     elseif nRows>1 && issorted(order, 'strictdescend')
-        error('The %s metadata for data source %s is in the opposite order of the %s metadata in .grid file %s.', metaDims(d), source.file, metaDims(d), obj.file );
+        error('The %s metadata for data source %s is in the opposite order of the %s metadata in .grid file %s.', metaDims(d), source.source, metaDims(d), obj.file );
     elseif ~issorted(order, 'strictascend')
-        error('The %s metadata for data source %s is in a different order than the %s metadata in .grid file %s.', metaDims(d), source.file, metaDims(d), obj.file );
+        error('The %s metadata for data source %s is in a different order than the %s metadata in .grid file %s.', metaDims(d), source.source, metaDims(d), obj.file );
     elseif nRows>1 && ~isequal(unique(diff(order)), 1)
-        error('The %s metadata for data source %s skips elements that are in the %s metadata for .grid file %s.', metaDims(d), source.file, metaDims(d), obj.file );
+        error('The %s metadata for data source %s skips elements that are in the %s metadata for .grid file %s.', metaDims(d), source.source, metaDims(d), obj.file );
     end
     
     % Record the limits of the source data dimensions in the .grid file
@@ -151,13 +157,13 @@
 higher = all(dimLimit>obj.dimLimit(:,2,:), 2);
 overlap = all(~(lower|higher), 1);
 if any(overlap)
-    error('The data in new source file %s overlaps data in file %s, which is already in .grid file %s.', source.file, obj.source.file(find(overlap,1),:), obj.file);
+    error('The data in new source %s overlaps data source %s, which is already in .grid file %s.', source.source, obj.source.source(find(overlap,1),:), obj.file);
 end
 
 % Convert the dataSource object into a structure of primitives and
 % implement the desired filepath style
 source = gridfile.convertSourceToPrimitives(source);
-source.file = obj.sourceFilepath(source.file, absolute);
+source.source = obj.sourceFilepath(source.source, absolute);
 
 % Preallocate the length of each of the primitive fields
 sourceFields = fields(obj.source);
diff --git a/@gridfile/buildSourcesForFiles.m b/@gridfile/buildSourcesForFiles.m
index 59f387b5..9aee95ca 100644
--- a/@gridfile/buildSourcesForFiles.m
+++ b/@gridfile/buildSourcesForFiles.m
@@ -38,7 +38,7 @@
     % Provide extra error information if the data source file is missing
     catch ME
         if strcmp(ME.identifier, "DASH:missingFile")
-            error('Cannot find data source file "%s". It may have been moved, renamed, or deleted. If the file was moved or renamed, see "gridfile.renameSources" to update the data source file path.', filenames(s));
+            error('Cannot find data source "%s". It may have been moved, renamed, or deleted. If the file was moved or renamed, see "gridfile.renameSources" to update the data source file path.', filenames(s));
         end
         rethrow(ME);
     end
diff --git a/@gridfile/collectFullPaths.m b/@gridfile/collectFullPaths.m
index 795b635e..2079a325 100644
--- a/@gridfile/collectFullPaths.m
+++ b/@gridfile/collectFullPaths.m
@@ -16,10 +16,13 @@
 % paths: A string vector of absolute file paths.
 
 % Get the file names
-paths = obj.collectPrimitives("file", s);
+paths = obj.collectPrimitives("source", s);
+
+% Get the .grid file folders
+gridPath = fileparts(obj.file);
+gridFolders = split(gridPath, filesep);
 
 % Append the .grid file path to relative paths
-gridFolders = split(obj.file, filesep);
 for f = 1:numel(paths)
     file = char(paths(f));
     if file(1)=='.'
diff --git a/@gridfile/convertSourceToPrimitives.m b/@gridfile/convertSourceToPrimitives.m
index 4f77b322..302c1c2f 100644
--- a/@gridfile/convertSourceToPrimitives.m
+++ b/@gridfile/convertSourceToPrimitives.m
@@ -18,7 +18,7 @@
 s = struct();
 
 % Convert strings to chars
-s.file = char(source.file);
+s.source = char(source.source);
 s.var = char(source.var);
 s.dataType = char(source.dataType);
 
@@ -37,6 +37,8 @@
     s.type = 'nc';
 elseif isa(source, 'matSource')
     s.type = 'mat';
+elseif isa(source, 'opendapSource')
+    s.type = 'opendap';
 end
 
 % Post-processing fields
diff --git a/@gridfile/findFileSources.m b/@gridfile/findFileSources.m
index 0b41fbfd..ae1ee240 100644
--- a/@gridfile/findFileSources.m
+++ b/@gridfile/findFileSources.m
@@ -13,7 +13,7 @@
 % matchesFile: A logical vector indicating which sources have the file name (nSource x 1).
 
 % Get the file names for the sources
-sourceFile = obj.collectPrimitives("file");
+sourceFile = obj.collectPrimitives("source");
 nSource = numel(sourceFile);
 
 % Remove paths
diff --git a/@gridfile/info.m b/@gridfile/info.m
index 8b2a6b7e..0051b860 100644
--- a/@gridfile/info.m
+++ b/@gridfile/info.m
@@ -105,13 +105,13 @@
     
     % Source output structure
     if nargout~=0
-        inputs(2:2:end) = {sources{s}.file, sources{s}.var, sourceDims, sourceSize, ...
+        inputs(2:2:end) = {sources{s}.source, sources{s}.var, sourceDims, sourceSize, ...
             sourceMeta, sources{s}.fill, sources{s}.range, sources{s}.convert};
         sourceInfo(s) = struct(inputs{:});
         
     % Print source to console
     else
-        [~, name, ext] = fileparts(sources{s}.file);
+        [~, name, ext] = fileparts(sources{s}.source);
         fprintf('The variable %s in file %s is a data source.\n', sources{s}.var, strcat(name, ext));
         if ~isnan(sources{s}.fill)
             fprintf('The fill value is %s.\n', num2str(sources{s}.fill));
diff --git a/@gridfile/renameSources.m b/@gridfile/renameSources.m
index 3eb89bdc..d09f23e5 100644
--- a/@gridfile/renameSources.m
+++ b/@gridfile/renameSources.m
@@ -113,20 +113,20 @@
 % Convert the new file names to primitives. Update primitive array size
 newname = char(newname);
 newMax = size(newname, 2);
-f = strcmp('file', fields(obj.source));
+f = strcmp('source', fields(obj.source));
 
 if obj.maxLength(f) < newMax
     obj.maxLength(f) = newMax;
-    obj.source.file = gridfile.padPrimitives(obj.source.file, newMax);
+    obj.source.source = gridfile.padPrimitives(obj.source.source, newMax);
 else
     newname = gridfile.padPrimitives(newname, obj.maxLength(f));
 end
 
 % Rename the sources. Save to .grid file
-[~, k] = ismember('file', fields(obj.source));
+[~, k] = ismember('source', fields(obj.source));
 for f = 1:nFile
     s = find(fileSources(:,f));
-    obj.source.file(s,:) = newname(f,:);
+    obj.source.source(s,:) = newname(f,:);
     obj.fieldLength(s,k) = newLength(f);
     obj.absolutePath(s) = absolutePath(f);
 end
diff --git a/@gridfile/repeatedLoad.m b/@gridfile/repeatedLoad.m
index 0f7acec7..856c71b0 100644
--- a/@gridfile/repeatedLoad.m
+++ b/@gridfile/repeatedLoad.m
@@ -101,7 +101,7 @@
     end
     
     % Load the data from the data source. Match .grid dimension order
-    Xsource = source.read( sourceIndices );
+    [Xsource, sources{useSource(s)}] = source.read( sourceIndices );
     [~, index] = ismember(source.mergedDims, obj.dims);
     X(outputIndices{:}) = dash.permuteDimensions(Xsource, index, false, nDims);
 end
diff --git a/@gridfile/sourceFilepath.m b/@gridfile/sourceFilepath.m
index 8c5e7620..6e1e8344 100644
--- a/@gridfile/sourceFilepath.m
+++ b/@gridfile/sourceFilepath.m
@@ -16,7 +16,7 @@
 % path: The file path for the .grid file.
 
 if ~absolute
-    path = dash.relativePath( path, obj.file );
+    path = dash.relativePath( path, fileparts(obj.file) );
 end
 path = dash.unixStylePath(path);
 
diff --git a/@stateVector/sequence.m b/@stateVector/sequence.m
index b6e6bff9..0d57ef2b 100644
--- a/@stateVector/sequence.m
+++ b/@stateVector/sequence.m
@@ -31,8 +31,7 @@
 %    one dimension listed in dims. Must be in the same dimension order as
 %    dims.
 %
-% metadata: Metadata for the sequence. Either a vector with one element per
-%    sequence index or an array with one row per sequence index.
+% metadata: Metadata for the sequence. An array with one row per sequence index.
 %
 % metadataCell: A cell vector. Each element contains the metadata for one
 %    dimension listed in dims. Must be in the stame dimension order as dims
diff --git a/@stateVectorVariable/sequence.m b/@stateVectorVariable/sequence.m
index 12ac48bc..bf8764ff 100644
--- a/@stateVectorVariable/sequence.m
+++ b/@stateVectorVariable/sequence.m
@@ -26,8 +26,7 @@
 %    one dimension listed in dims. Must be in the same dimension order as
 %    dims.
 %
-% metadata: Metadata for the sequence. Either a vector with one element per
-%    sequence index or an array with one row per sequence index.
+% metadata: Metadata for the sequence. An array with one row per sequence index.
 %
 % metadataCell: A cell vector. Each element contains the metadata for one
 %    dimension listed in dims. Must be in the same dimension order as dims
@@ -56,14 +55,12 @@
     end
     obj.assertAddIndices(indices{k}, d(k), name);
     
-    % Error check metadata
-    errorStrs = ['array', 'row'];
-    if isvector(metadata{k})
-        errorStrs = ['vector', 'element'];
-        metadata{k} = metadata{k}(:);
-    end
+    % Check metadata is allowed type. Convert cellstring to string
+    metadata{k} = gridfile.checkMetadataField(metadata{k}, dims(k));
+    
+    % Metadata rows
     if size(metadata{k},1)~=numel(indices{k})
-        metadataSizeError( obj, dims(k), errorStrs, numel(indices{k}), size(metadata{k},1) );
+        metadataSizeError( obj, dims(k), numel(indices{k}), size(metadata{k},1) );
     end
 
     % Update
@@ -81,8 +78,8 @@
     'ensemble dimension, see "stateVector.design".'], obj.dims(bad), ...
     obj.name, obj.dims(bad));
 end
-function[] = metadataSizeError(obj, dim, strs, nIndex, nRows)
-error(['When metadata is a %s, it must have one %s per sequence index (%.f), ',...
-    'but the metadata for dimension %s in variable %s currently has %.f %ss.'], ...
-    strs(1), strs(2), nIndex, dim, obj.name, nRows, strs(2));
+function[] = metadataSizeError(obj, dim, nIndex, nRows)
+error(['Sequence metadata must have one row per sequence index (%.f), ',...
+    'but the metadata for dimension "%s" in variable "%s" currently has %.f rows.'], ...
+    nIndex, dim, obj.name, nRows);
 end
\ No newline at end of file
diff --git a/@stateVectorVariable/specifyMetadata.m b/@stateVectorVariable/specifyMetadata.m
index 8b53b770..46917296 100644
--- a/@stateVectorVariable/specifyMetadata.m
+++ b/@stateVectorVariable/specifyMetadata.m
@@ -18,7 +18,7 @@
 % obj: The updated stateVectorVariable object
 
 % Error check, dimension index. Cannot conflict with metadata conversion
-d = obj.checkDimensions(dim, false);
+[d, dim] = obj.checkDimensions(dim, false);
 if any(obj.convert(d))
     previousMetadataError(obj, d);
 end
diff --git a/dataSource.m b/dataSource.m
index d7389b6f..0957dd82 100644
--- a/dataSource.m
+++ b/dataSource.m
@@ -1,12 +1,12 @@
 classdef (Abstract) dataSource
-    %% Implements an object that can extract information from a data source
-    % file. dataSource is an abstract class. Concrete subclasses
-    % implement functionality for different types of data files. (For
-    % example, netCDF and .mat files).
+    %% Implements an object that can extract information from a data source.
+    % dataSource is an abstract class. Concrete subclasses
+    % implement functionality for different types of data sourcess. (For
+    % example, netCDF and .mat files and opendap files).
     
     properties
-        file;  % The file name
-        var;   % The name of the variable in the file
+        source; % The data source. A filename or opendap url
+        var; % (For hdf data sources) The name of the variable.
         dataType;  % The type of data in the file.
         unmergedDims;  % The order of the dimensions in the file
         unmergedSize; % The size of the original data in the file
@@ -22,24 +22,17 @@
         subclassResponsibilities = ["dataType", "unmergedSize"];
     end
     
-    % Constructor and object methods.
+    % Constructor methods and error checking
     methods
-        function[obj] = dataSource(file, var, dims, fill, range, convert)
+        function[obj] = dataSource(source, sourceName, dims, fill, range, convert)
             %% Class constructor for a dataSource object. dataSource is an 
             % abstract class, so this provides constructor operations necessary
             % for any data source.
             %
-            % obj = dataSource(file, var, dims, fill, range, convert)
+            % obj = dataSource(dims, fill, range, convert)
             %
             % ----- Inputs -----
             %
-            % file: The name of the data source file. A string. If only the file name is
-            %    specified, the file must be on the active path. Use the full file name
-            %    (including path) to add a file off the active path. All file names
-            %    must include the file extension.
-            %
-            % var: The name of the variable in the source file.
-            %
             % dims: The order of the dimensions of the variable in the source file. A
             %    string or cellstring vector.
             %
@@ -56,11 +49,9 @@
             %    multiplicative constant (a). The second element specifieds the
             %    additive constant (b).
             
-            % Error check strings, vectors
-            file = dash.assertStrFlag(file, "file");
-            var = dash.assertStrFlag(var, "var");
+            % Error check strings, vectors.
+            source = dash.assertStrFlag(source, sourceName);
             dims = dash.assertStrList(dims, "dims");
-            file = dash.checkFileExists(file);
             
             % Error check the post-processing values
             if ~isnumeric(fill) || ~isscalar(fill)
@@ -78,46 +69,145 @@
             end
             
             % Save properties
-            obj.file = file;
-            obj.var = var;
+            obj.source = source;
             obj.unmergedDims = dims;        
             obj.fill = fill;
             obj.range = range;
             obj.convert = convert;
                         
-        end        
-        function[] = checkVariable( obj, fileVariables )
-            %% Returns an error message when a data source file does not contain
-            % the specified data source variable.
+        end    
+        function[obj] = checkFile(obj)
+            %% Checks the data source is a file that exists
+            obj.source = dash.checkFileExists(obj.source);
+        end
+        function[obj] = setVariable(obj, var)
+            %% For hdf data sources, sets the variable name
+            obj.var = dash.assertStrFlag(var, 'var');
+        end
+        function[] = checkVariableInSource(obj, sourceVariables)
+            %% Checks that a variable is in a data source
+            if ~ismember(obj.var, sourceVariables)
+                error('The data source "%s" does not have a %s variable', obj.source, obj.var);
+            end
+        end
+    end
+    
+    % Static method used to select concrete dataSource subclasses
+    methods (Static)
+        function[source] = new(type, file, var, dims, fill, range, convert)
+            %% Creates a new dataSource object. dataSource is an abstract
+            % class, so this method routes to the constructor of the
+            % appropriate subclass.
             %
-            % obj.checkVariable(fileVariables);
+            % source = dataSource.new(type, file, var, dims, fill, range, convert)
             %
             % ----- Inputs -----
             %
-            % fileVariables: A list a variables in the data source file. A
-            %    string vector or cellstring vector.
+            % type: The type of data source. A string. 
+            %    "nc": Use when the data source is a NetCDF file.
+            %    "mat": Use when the data source is a .mat file.
+            %    "opendap": Use when the data source is an OPeNDAP NetCDF
+            %
+            % file: The name of the data source file. A string. If only the file name is
+            %    specified, the file must be on the active path. Use the full file name
+            %    (including path) to add a file off the active path. All file names
+            %    must include the file extension.
+            %
+            % var: The name of the variable in the source file.
+            %
+            % dims: The order of the dimensions of the variable in the source file. A
+            %    string or cellstring vector.
+            %
+            % fill: A fill value. Must be a scalar. When data is loaded from the file, 
+            %    values matching fill are converted to NaN. 
+            %
+            % range: A valid range. A two element vector. The first element is the
+            %    lower bound of the valid range. The second elements is the upper bound
+            %    of the valid range. When data is loaded from the file, values outside
+            %    of the range are converted to NaN.
+            %
+            % convert: Applies a linear transformation of form: Y = aX + b
+            %    to loaded data. A two element vector. The first element specifies the
+            %    multiplicative constant (a). The second element specifieds the
+            %    additive constant (b).
+            
+            % Error check type
+            type = dash.assertStrFlag(type, 'type');
+            
+            % Set defaults for optional values
+            if ~exist('fill','var') || isempty(fill)
+                fill = NaN;
+            end
+            if ~exist('range','var') || isempty(range)
+                range = [-Inf Inf];
+            end
+            if ~exist('convert','var') || isempty(convert)
+                convert = [1 0];
+            end
+            
+            % Create the concrete dataSource object. This will error check
+            % and get the size of the raw unmerged data in the source.
+            if strcmpi(type,'nc')
+                source = ncSource(file, 'file', var, dims, fill, range, convert);
+            elseif strcmpi(type, 'mat')
+                source = matSource(file, var, dims, fill, range, convert);
+            elseif strcmpi(type, 'opendap')
+                source = opendapSource(file, var, dims, fill, range, convert);
+            else
+                error('type must be one of the strings "nc", "mat", or "opendap".');
+            end
+            
+            % Check that the subclass constructor set all fields for which
+            % it is responsible
+            fields = dataSource.subclassResponsibilities;
+            for f = 1:numel(fields)
+                if isempty( source.(fields(f)) )
+                    error('The dataSource subclass constructor did not set the "%s" property.', fields(f));
+                end
+            end
+            
+            % Ensure all non-trailing singleton dimensions are named. Pad
+            % the unmerged size for any named trailing singletons.
+            nDims = numel(source.unmergedDims);
+            minimumDims = max( [1, find(source.unmergedSize~=1,1,'last')] );            
+            if nDims < minimumDims
+                error('The first %.f dimensions of variable %s in file %s require names, but dims only contains %.f elements',minimumDims, obj.var, obj.file, numel(obj.dims) );
+            elseif numel(source.unmergedSize) < nDims
+                source.unmergedSize( end+1:nDims ) = 1;
+            end
             
-            infile = ismember(obj.var, fileVariables);
-            if ~infile
-                error('File %s does not contain a %s variable.', obj.file, obj.var);
-            end    
-        end  
-        function[X] = read( obj, mergedIndices )
-        %% Reads values from a data source.
-        %
-        % X = obj.read( mergedIndices )
-        %
-        % ----- Inputs -----
-        %
-        % mergedIndices: A cell array. Each element contains the indices to read 
-        %    for one dimension. Dimensions must be in the same order as the merged
-        %    dimensions. Indices should be linear indices along the dimension.
-        %
-        % ----- Outputs -----
-        %
-        % X: The values read from the data source file. Dimensions are in
-        %    the order of the merged dimensions.
-        
+            % Get the merge map and merged data size
+            source.mergedDims = unique(source.unmergedDims, 'stable');
+            nUniqueDims = numel(source.mergedDims);
+            source.merge = NaN(1,nDims);
+            source.mergedSize = NaN(1,nUniqueDims);
+            
+            for d = 1:nUniqueDims
+                isdim = find( strcmp(source.mergedDims(d), source.unmergedDims) );
+                source.merge(isdim) = d;
+                source.mergedSize(d) = prod( source.unmergedSize(isdim) );
+            end
+        end
+    end
+          
+    % Interface used to read data from a dataSource
+    methods
+        function[X, obj] = read( obj, mergedIndices )
+            %% Reads values from a data source.
+            %
+            % X = obj.read( mergedIndices )
+            %
+            % ----- Inputs -----
+            %
+            % mergedIndices: A cell array. Each element contains the indices to read 
+            %    for one dimension. Dimensions must be in the same order as the merged
+            %    dimensions. Indices should be linear indices along the dimension.
+            %
+            % ----- Outputs -----
+            %
+            % X: The values read from the data source file. Dimensions are in
+            %    the order of the merged dimensions.
+
             % Preallocate
             nMerged = numel(obj.mergedDims);
             nUnmerged = numel(obj.unmergedDims);
@@ -138,8 +228,9 @@
                 [unmergedIndices{isdim}] = ind2sub(siz, mergedIndices{d});
             end
 
-            % Currently, all data source (.mat and netCDF) can only load equally spaced
+            % Currently, all data source (.mat and netCDF based) can only load equally spaced
             % values. Get equally spaced indices to load from each source.
+            % (This may eventually be merged into hdfSource).
             for d = 1:nUnmerged
                 uniqueIndices = unique(sort(unmergedIndices{d}));
                 loadIndices{d} = dash.equallySpacedIndices(uniqueIndices);
@@ -156,11 +247,11 @@
             end
 
             % Load the values from the data source
-            X = obj.load( loadIndices );
+            [X, obj] = obj.load( loadIndices );
 
             % Track which dimensions become singletons via merging
             remove = NaN(1, nUnmerged-nMerged);
-            
+
             % Permute dimensions being merged to the front
             for d = 1:nMerged
                 order = 1:nUnmerged;
@@ -174,14 +265,14 @@
                 siz = size(X);
                 nDim = numel(isdim);
                 siz(end+1:nDim) = 1;
-                
+
                 newSize = [prod(siz(1:nDim)), ones(1,nDim-1), siz(nDim+1:end)];
                 X = reshape(X, newSize);
 
                 % Unpermute and note if any dimensions should be removed
                 [~, reorder] = sort(order);
                 X = permute( X, reorder );
-                
+
                 k = find(isnan(remove), 1, 'first');
                 remove(k:k+nDim-2) = isdim(2:end);
 
@@ -199,128 +290,32 @@
             dimOrder = 1:nUnmerged;
             order = [dimOrder(~ismember(dimOrder,remove)), remove];
             X = permute(X, order);
-            
+
             % Remove any unrequested data elements that were loaded to
             % fulfill equal spacing requirements
             X = X(keepElements{:});
-            
+
             % Convert fill value to NaN
             if ~isnan(obj.fill)
                 X(X==obj.fill) = NaN;
             end
-            
+
             % Convert values outside the valid range to NaN
             if ~isequal(obj.range, [-Inf Inf])
                 valid = (X>=obj.range(1)) & (X<=obj.range(2));
                 X(~valid) = NaN;
             end
-            
+
             % Apply linear transformation
             if ~isequal(obj.convert, [1 0])
                 X = obj.convert(1)*X + obj.convert(2);
             end
         end
     end
-    
-    % Create new dataSource subclass
-    methods (Static)
-        function[source] = new(type, file, var, dims, fill, range, convert)
-            %% Creates a new dataSource object. dataSource is an abstract
-            % class, so this method routes to the constructor of the
-            % appropriate subclass.
-            %
-            % source = dataSource.new(type, file, var, dims, fill, range, convert)
-            %
-            % ----- Inputs -----
-            %
-            % type: The type of data source. A string. 
-            %    "nc": Use when the data source is a NetCDF file.
-            %    "mat": Use when the data source is a .mat file.
-            %
-            % file: The name of the data source file. A string. If only the file name is
-            %    specified, the file must be on the active path. Use the full file name
-            %    (including path) to add a file off the active path. All file names
-            %    must include the file extension.
-            %
-            % var: The name of the variable in the source file.
-            %
-            % dims: The order of the dimensions of the variable in the source file. A
-            %    string or cellstring vector.
-            %
-            % fill: A fill value. Must be a scalar. When data is loaded from the file, 
-            %    values matching fill are converted to NaN. 
-            %
-            % range: A valid range. A two element vector. The first element is the
-            %    lower bound of the valid range. The second elements is the upper bound
-            %    of the valid range. When data is loaded from the file, values outside
-            %    of the range are converted to NaN.
-            %
-            % convert: Applies a linear transformation of form: Y = aX + b
-            %    to loaded data. A two element vector. The first element specifies the
-            %    multiplicative constant (a). The second element specifieds the
-            %    additive constant (b).
-            
-            % Check the type is allowed
-            if ~dash.isstrflag(type) || ~ismember(type, ["nc","mat"])
-                error('type must be either the string "nc" or "mat".');
-            end
-            
-            % Set defaults for optional values
-            if ~exist('fill','var') || isempty(fill)
-                fill = NaN;
-            end
-            if ~exist('range','var') || isempty(range)
-                range = [-Inf Inf];
-            end
-            if ~exist('convert','var') || isempty(convert)
-                convert = [1 0];
-            end
-            
-            % Create the subclass dataSource object. This will error check
-            % file, var, and dims and get the size of the raw unmerged data
-            % in the source.
-            if strcmp(type,'nc')
-                source = ncSource(file, var, dims, fill, range, convert);
-            elseif strcmp(type, 'mat')
-                source = matSource(file, var, dims, fill, range, convert);
-            end
-            
-            % Check that the subclass constructor set all fields for which
-            % it is responsible
-            fields = dataSource.subclassResponsibilities;
-            for f = 1:numel(fields)
-                if isempty( source.(fields(f)) )
-                    error('The dataSource subclass constructor did not set the "%s" property.', fields(f));
-                end
-            end
-            
-            % Ensure all non-trailing singleton dimensions are named. Pad
-            % the unmerged size for any named trailing singletons.
-            nDims = numel(source.unmergedDims);
-            minimumDims = max( [1, find(source.unmergedSize~=1,1,'last')] );            
-            if nDims < minimumDims
-                error('The first %.f dimensions of variable %s in file %s require names, but dims only contains %.f elements',minimumDims, obj.var, obj.file, numel(obj.dims) );
-            elseif numel(source.unmergedSize) < nDims
-                source.unmergedSize( end+1:nDims ) = 1;
-            end
-            
-            % Get the merge map and merged data size
-            source.mergedDims = unique(source.unmergedDims, 'stable');
-            nUniqueDims = numel(source.mergedDims);
-            source.merge = NaN(1,nDims);
-            source.mergedSize = NaN(1,nUniqueDims);
-            
-            for d = 1:nUniqueDims
-                isdim = find( strcmp(source.mergedDims(d), source.unmergedDims) );
-                source.merge(isdim) = d;
-                source.mergedSize(d) = prod( source.unmergedSize(isdim) );
-            end
-        end
-    end
-    
-    % Subclasses must load values from data source files
+
+    % Concrete subclasses must be able to load data from requested indices
     methods (Abstract)
-        X = load(obj, indices);
+        [X, obj] = load(obj, indices);
     end
     
 end
\ No newline at end of file
diff --git a/matSource.m b/matSource.m
index 5c7481db..af829ee4 100644
--- a/matSource.m
+++ b/matSource.m
@@ -1,5 +1,5 @@
 classdef matSource < dataSource
-    %% Implements a data source object that can read values from .mat files.
+    %% Reads data from a .mat file data source
     
     properties
         m; % A matfile object
@@ -11,35 +11,41 @@
     
     methods
         function obj = matSource(file, var, dims, fill, range, convert)
-            %% Creates a new matSource object.
+            %% Creates a new matSource object. Checks the matfile is valid
+            % and contains the required variable
             %
             % obj = matSource(file, var, dims, fill, range, convert)
             %
             % ----- Inputs -----
             %
-            % See the documentation in dataSource.new
+            % file: The name of the .mat file. A string.
+            %
+            % var: The name of the variable in the .mat file. A string.
+            %
+            % dims, fill, range, convert: See the documentation in dataSource
             %
             % ----- Outputs -----
             %
-            % obj: A new matSource object.
+            % obj: The new matSource object
             
-            % First call the data source constructor for initial error
-            % checking and to save the input args
-            obj@dataSource(file, var, dims, fill, range, convert);
+            % Constructor and error checks
+            obj@dataSource(file, 'file', dims, fill, range, convert);
+            obj = obj.checkFile;
+            obj = obj.setVariable(var);
             
-            % Matfile access is via chars
+            % Use chars to access matfile variables
             obj.var = char(obj.var);
             
-            % Check that the file is a matfile
+            % Check the file is a matfile
             try
-                obj.m = matfile(file);
+                obj.m = matfile(obj.source);
             catch
-                error('The file %s is not a valid .mat file.', file);
+                error('The file %s is not a valid .mat file.', obj.source);
             end
             
             % Check the variable is in the file
             fileVariables = string(who(obj.m));
-            obj.checkVariable( fileVariables );
+            obj.checkVariableInSource(fileVariables);
             
             % Get the data type and size of the array
             info = whos(obj.m, obj.var);
@@ -48,17 +54,20 @@
             
             % Warn the user if this is not v7.3
             warn = warning('query', obj.warnID);
-            warning('error', obj.warnID); %#ok<CTPCT>
+            warning('error', obj.warnID);
             firstIndex = repmat({1}, [1, numel(obj.unmergedSize)]);
             try
                 obj.m.(obj.var)(firstIndex{:});
             catch
-                warning('File %s is not a version 7.3 .mat file. Version 7.3 is STRONGLY recommended for use with dash. Consider saving .mat files with the ''-v7.3'' flag or use dash.convertToV7_3 to convert existing .mat files to a v7.3 format. For more details, see the Matlab documention on "save" and "MAT-File versions".', obj.file);
+                warning(['File %s is not a version 7.3 .mat file. Version 7.3 ',...
+                    'is STRONGLY recommended for use with DASH. Consider saving .mat files ',...
+                    'with the ''-v7.3'' flag or use dash.convertToV7_3 to convert existing .mat ',...
+                    'files to a v7.3 format. For more details, see the Matlab documention on "save" ',...
+                    'and "MAT-File versions".'], obj.source);
             end
-            warning( warn.state, obj.warnID );  
-            
-        end        
-        function[X] = load( obj, indices )
+            warning( warn.state, obj.warnID );
+        end
+        function[X, obj] = load( obj, indices )
             %% Loads data from a .mat data source.
             %
             % X = obj.load(indices)
@@ -74,9 +83,11 @@
             %
             % X: The data located at the requested indices.
             
-            % Disable the partial load warning and load
+            % Disable the partial load warning
             warn = warning('query', obj.warnID);
             warning('off', obj.warnID);
+            
+            % Load the data
             X = obj.m.(obj.var)(indices{:});
             
             % Restore the original warning state
diff --git a/ncSource.m b/ncSource.m
index 43ee5de1..1885aebd 100644
--- a/ncSource.m
+++ b/ncSource.m
@@ -1,48 +1,41 @@
 classdef ncSource < dataSource
-    %% Implements a data source object that can read values from a netCDF file.
+    %% Used to read data from source based on a NetCDF format. Includes 
+    % local NetCDF files and OPeNDAP requests.
     
     properties
-        nDims; % The number of defined dimensions for the variable in the netCDF
+        nDims; % The number of dimensions recorded in the NetCDF
     end
     
     methods
-        function obj = ncSource(file, var, dims, fill, range, convert)
-            %% Creates a new ncSource object.
-            %
-            % obj = ncSource(file, var, dims, fill, range, convert)
-            %
-            % ----- Inputs -----
-            %
-            % See the documentation in dataSource.new
-            %
-            % ----- Outputs -----
-            %
-            % obj: A new ncSource object
+        function obj = ncSource(source, sourceName, var, dims, fill, range, convert)
             
-            % First call the data source constructor for initial error
-            % checking and to save the input args
-            obj@dataSource(file, var, dims, fill, range, convert);
+            % Constructor and error checking
+            obj@dataSource(source, sourceName, dims, fill, range, convert);
+            obj = obj.setVariable(var);
+            if strcmp(sourceName, 'file')
+                obj = obj.checkFile;
+            end
             
-            % Check the file is actually a NetCDF
+            % Check the source is actually a NetCDF
             try
-                info = ncinfo( obj.file );
+                info = ncinfo(obj.source);
             catch
-                error('The file %s is not a valid NetCDF file.', obj.file );
+                error('The data source "%s" is not a valid NetCDF file.', obj.source);
             end
             
-            % Check that the variable is in the file
+            % Check the variable is in the file. Get the list of variables.
             nVars = numel(info.Variables);
             fileVariables = cell(nVars,1);
             [fileVariables{:}] = deal( info.Variables.Name );
-            obj.checkVariable( fileVariables );
+            obj.checkVariableInSource(fileVariables);
             
             % Get the data type and size of the array
             [~,v] = ismember(obj.var, fileVariables);
             obj.dataType = info.Variables(v).Datatype;
             obj.unmergedSize = info.Variables(v).Size;
             obj.nDims = numel(info.Variables(v).Dimensions);
-        end        
-        function[X] = load(obj, indices)
+        end
+        function[X, obj] = load(obj, indices)
             %% Loads data from a netCDF data source.
             %
             % X = obj.load(indices)
@@ -73,8 +66,8 @@
             end
             
             % Load the data
-            X = ncread( obj.file, obj.var, start, count, stride ); 
+            X = ncread( obj.source, obj.var, start, count, stride ); 
         end
     end
     
-end
\ No newline at end of file
+end
diff --git a/opendapSource.m b/opendapSource.m
new file mode 100644
index 00000000..e3848830
--- /dev/null
+++ b/opendapSource.m
@@ -0,0 +1,72 @@
+classdef opendapSource < ncSource
+    %% Reads data accessed via an OPeNDAP url. Attempts to load and save 
+    % the entire variable when using repeated loads to increase speed.
+    
+    properties
+        X; % The loaded and saved dataset
+        attemptFullLoad; % Whether to attempt to load the entire dataset
+        saved; % Whether the dataset is currently saved
+    end
+    
+    methods
+        function obj = opendapSource(url, var, dims, fill, range, convert)
+            %% Creates a new opendapSource. Checks the url links to a valid
+            % netcdf file that contains the specified variable.
+            %
+            % obj = opendapSource(url, var, dims, fill, range, convert)
+            %
+            % ----- Inputs -----
+            %
+            % url: The OPeNDAP url. A string.
+            %
+            % var: The name of the variable in the OPeNDAP NetCDF. A string
+            %
+            % dims, fill, range, convert: See the documentation in dataSource
+            %
+            % ----- Outputs -----
+            %
+            % obj: The new opendapSource object
+            
+            % Superclass constructors
+            obj@ncSource(url, false, var, dims, fill, range, convert);
+            
+            % Track status of loading the entire dataset
+            obj.attemptFullLoad = true;
+            obj.saved = false;
+        end
+        function[X, obj] = load(obj, indices)
+            %% Load data from an OPeNDAP data source.
+            %
+            % X = obj.load(indices)
+            %
+            % ----- Inputs -----
+            %
+            % indices: A cell array. Each element contains the linear 
+            %    indices to load for a dimension. Indices must be equally
+            %    spaced and monotonically increasing. Dimensions must be in
+            %    the order of the unmerged dimensions.
+            %
+            % ----- Outputs -----
+            %
+            % X: The data located at the requested indices.
+            
+            % Attempt to load the entire dataset once
+            if obj.attemptFullLoad
+                try
+                    obj.X = ncread(obj.source, obj.var);
+                    obj.saved = true;
+                catch
+                end
+                obj.attemptFullLoad = false;
+            end
+            
+            % If saved, load directly. Otherwise, use ncread
+            if obj.saved
+                X = obj.X(indices{:});
+            else
+                [X, obj] = load@ncSource(obj, indices);
+            end
+        end
+    end
+    
+end
\ No newline at end of file