gplx/mediawiki/extensions/SemanticMediaWiki/docs/architecture/querying.data.md

Querying and displaying data

When resolving a query request (i.e. resolving the parser function {{#ask ... }} or {{#show: ... }}) the QueryEngine has two distinct tasks to accomplish:

• First, build a query condition in a corresponding language (SQL, ES-DSL, SPARQL) that is understood by the assigned QueryEngine where it returns a list of subjects that match the condition (similar to finding rows in a table that match a WHERE condition)
• Secondly, build a QueryResult object that contains the matched subjects and provide information on the requested printouts (equivalent of columns displayed in a table)

src/ParserFunctions

• AskParserFunction.php defines the #ask parser function
• ShowParserFunction.php defines the #show parser function

src/Query

• Parser.php interface to src/Query/Parser to create a Description and Query object from an {{#ask: ...}} string
• PrintRequest.php
• ResultPrinter.php interface to concrete implementations found in src/Query/ResultPrinters

src/Query/Language

Each condition element (e.g. [[Has foo::bar]] || [[!Foo]]) of a query is represented by a Description object allowing to express a query condition as as description AST.

• Description.php

src/Query/Result

• [QueryResult.php] the instance represents the matched subjects of a query request (i.e. rows of a table)
• [ResultArray.php] represents a lazy-object to contain the printouts (see PrintRequest) for a particular subject (i.e. as columns for a particular row)

src/Query/ResultPrinters

A ResultPrinter is the user facing output formatter that takes a QueryResult and transform its representation into a specific format by extending:

• ResultPrinter.php is an abstract base class to provide accessors and pre and postprocess the output after an individual printer returns the formatted result or
• FileExportPrinter.php is an abstract base class for file export result printers

Examples

• boilerplate.resultprinter starting point for writing a result printer
• boilerplate.fileexportprinter starting point for writing a file result printer
• boilerplate.resultprinter.example a complete example
• query.description.md how to build a Descripion objects
• query.someproperty.of.type.number.md example on how to query a number