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Connector Operations

This document will provided a detailed description of the different operations that can be supported by a Crossdata connector.

Definition of Connector Operation

A connector operation defines a capability a connector provides. All connector operations must be declared in their associated manifest. As an example, consider the following InMemoryConnector.xml manifest

<?xml version="1.0" encoding="UTF-8"?>
<!-- This file contains the manifest for the connector. -->
<Connector>
    <!-- Name of the connector as it will be identified in Crossdata -->
    <ConnectorName>InMemoryConnector</ConnectorName>
    <!-- Define the list of datastore this connector is able to access. -->
    <DataStores>
        <DataStoreName>InMemoryDatastore</DataStoreName>
    </DataStores>
    <!-- Connector version -->
    <Version>0.3.0</Version>

    <!-- Define the set of required operations the user will be asked to input
    when attaching the connector -->

    <!--OptionalProperties>
        <Property>
            <PropertyName>TableRowLimit</PropertyName>
            <Description>Limit of rows allowed per table</Description>
        </Property>
    </OptionalProperties-->

    <!-- Define the list of operations supported by the connector.
    Check crossdata/doc/ConnectorOperations.md for more information. -->
    <SupportedOperations>
        <operation>CREATE_CATALOG</operation>
        <operation>DROP_CATALOG</operation>
        <operation>CREATE_TABLE</operation>
        <operation>DROP_TABLE</operation>
        <operation>TRUNCATE_TABLE</operation>
        <operation>INSERT</operation>
        <operation>PROJECT</operation>
        <operation>SELECT_OPERATOR</operation>
        <operation>SELECT_FUNCTIONS</operation>
        <operation>SELECT_ORDER_BY</operation>
        <operation>SELECT_LIMIT</operation>
        <operation>FILTER_PK_EQ</operation>
        <operation>FILTER_PK_GT</operation>
        <operation>FILTER_PK_LT</operation>
        <operation>FILTER_PK_GET</operation>
        <operation>FILTER_PK_LET</operation>
        <operation>FILTER_NON_INDEXED_EQ</operation>
        <operation>FILTER_NON_INDEXED_GT</operation>
        <operation>FILTER_NON_INDEXED_LT</operation>
        <operation>FILTER_NON_INDEXED_GET</operation>
        <operation>FILTER_NON_INDEXED_LET</operation>
        <operation>IMPORT_METADATA</operation>
        <operation>PAGINATION</operation>
    </SupportedOperations>
</Connector>

Each operation is associated with the methods found in IMetadataEngine, IStorageEngine, and IQueryEngine. The following section provides a detailed description of each operation organized by the type of operation.

Types of Operations

The connector operations are organized attending to the type of operation to be performed: Metadata, Storage, and Query. In order to simplify the definition of the different connector, two concepts are taken into account: column_type, and relationship.

The column type is identified by Crossdata during the query analysis with the following types:

column_type Description
PK The column is part of the primary key.
INDEXED The column is indexed.
NON_INDEXED The column is not indexed.
FUNCTION A function is associated with the column.

With respect to the relationship, Crossdata supports:

relationship Description
EQ Equals.
GT Greater than.
LT Less than.
GET Greater or equal than.
LET Less or equal than.
ASSIGN A value is to be assigned to a column.
MATCH Compare with a Lucene-like expression.
DISTINCT Distinct operator in a column.
LIKE Search for a specified pattern.
NOT_LIKE Opposite of LIKE operator.
IN Search value in a list of values.
NOT_IN Opposite of IN operator.
BETWEEN Select values within a range.
NOT_BETWEEN Opposite of BETWEEN operator.

Metadata

Metadata operations are those associated with the IMetadataEngine interface.

  • CREATE_CATALOG: Create new catalogs.
  • ALTER_CATALOG: Alter existing catalogs.
  • DROP_CATALOG: Delete existing catalogs.
  • CREATE_TABLE: Create a new table.
  • ALTER_TABLE: Alter the definition of an existing table.
  • DROP_TABLE: Drop an existing table.
  • CREATE_INDEX: Create a new index.
  • DROP_INDEX: Drop an existing index.

The next operations is related to Data Discovery.

  • IMPORT_METADATA: Provide metadata of the existent tables.

Storage

Storage operations are those associated with the IStorageEngine interface.

  • INSERT: Insert a new row in the datastore. By default inserts are considered upsert operations.
  • INSERT_IF_NOT_EXISTS: Insert a new row in the datastore if that row does not exist without the upsert behaviour.
  • DELETE_<column_type>_<relationship>: Delete rows for the given type of columns and relations.
  • UPDATE_<column_type>_<relationship>: Update rows for the give type of columns and relations.
  • TRUNCATE_TABLE: Truncate the contents of an existing table.

Query

Storage operations are those associated with the IQueryEngine interface.

  • ASYNC_QUERY: Support for asynchronous query execution.
  • PROJECT: Retrieve a set of columns from a specific table.
  • SELECT_OPERATOR: Select a set of output columns for a query with alias.
  • SELECT_WINDOW: Supports WINDOW clauses for streaming-like queries.
  • SELECT_LIMIT: Limit the number of output rows.
  • SELECT_<join_type>_JOIN: Support for INNER JOIN operations.
  • SELECT_<join_type>_JOIN_PARTIALS_RESULTS: Support for INNER JOIN with one source already defined.
  • SELECT_ORDER_BY: Support for ORDER BY clauses.
  • SELECT_GROUP_BY: Support for GROUP BY clauses.
  • SELECT_CASE_WHEN: Support for selecting a value with a CASE WHEN structure.
  • SELECT_FUNCTIONS: Support for using functions as a selector.
  • SELECT_SUBQUERY: Support for using virtual tables.
  • FILTER_<column_type>_<relationship>: Filter a column by a particular relationship.

The next type of joins are supported:

  • INNER
  • LEFT_OUTER
  • RIGHT_OUTER
  • FULL_OUTER
  • FULL_NATURAL
  • CROSS

More information

For more information, check the project documentation.