This document provides a short introduction into the database schema and table structure used by Semantic MediaWiki.

Database schema

The database schema is defined using the TableSchemaManager class and together with the TableBuilder is forming the interface to define, create, and remove database and schema related information used by Semantic MediaWiki.

The SPO (subject, predicate, and object) pattern paradigm is reflected in how semantic relations are organized in Semantic MediaWiki. Three table types are used to store information with table fields normally being identified by its related intent such as s_ (subject), p_ (predicate, property), and o_ (object).

The three table types are:

• Data table a table that to stores information not necessarily following the SPO pattern (statistics, ids, dependencies etc.)
• Property table (Common) a table (identified by smw_di_...) that follows the SPO pattern
• Property table (Fixed) a table (identified by smw_fpt_...) that follows the SPO pattern but omits the p_id as it is a designated table to one particular property

A special type are temporary tables only used during a search request (which remains in-memory) and is dropped as soon as a query is resolved.

Data tables

Data tables follow individual schema definitions to serve a specific purpose for either collecting or aggregating data.

• smw_object_ids contains the entity and object references and is holding the foreign key (smw_id field) for all other tables that use an ID reference.
• smw_query_links collects embedded query dependencies.
• smw_prop_stats a table that collects of property statistics.
• smw_ft_search if enabled, contains a collection of full-text indexable text components.

Property tables (Common)

User defined properties with an assigned datatype are stored in tables with a predefined structure and relevant fields required by the https://github.com/SemanticMediaWiki/SemanticMediaWiki/blob/master/docs/architecture/datamodel.dataitem.md "`DataItem`" to represent its literal value.

[
    DataItem::TYPE_NUMBER     => 'smw_di_number',
    DataItem::TYPE_BLOB       => 'smw_di_blob',
    DataItem::TYPE_BOOLEAN    => 'smw_di_bool',
    DataItem::TYPE_URI        => 'smw_di_uri',
    DataItem::TYPE_TIME       => 'smw_di_time',
    DataItem::TYPE_GEO        => 'smw_di_coords',
    DataItem::TYPE_CONTAINER  => 'smw_di_container',
    DataItem::TYPE_WIKIPAGE   => 'smw_di_wikipage',
    DataItem::TYPE_CONCEPT    => 'smw_conc'
]

Available fields include:

• s_id subject ID reference (see smw_id)
• p_id property ID reference (see smw_id)
• o_... fields that identify object related values to adhere the s-p-o pattern

Property tables (Fixed)

Fixed property table assignments are either defined by TypesRegistry.php (for predefined properties) or by the $smwgFixedProperties setting (for user-defined fixed properties).

Available fields include:

• s_id subject ID reference (see smw_id)
• o_... fields that identify object related values to adhere the s-p-o pattern

See also

• Working with and https://github.com/SemanticMediaWiki/SemanticMediaWiki/blob/master/docs/architecture/changing.tableschema.md "changing the table schema"