Getting Started

Install

To install SPARQLer just run

composer require madbob/sparqler

The full code, MIT licensed, is hosted on GitLab (and, of course, open to contributions!).

SPARQL 101

For reference and introduction, lets make a comparison among SQL and SPARQL.

An usual SQL query looks like:

SELECT column1, column2 FROM table WHERE column3 = 'something';

while an equivalent SPARQL query looks like:

SELECT ?foo ?bar WHERE ?item column1 ?foo . ?item column2 ?bar . ?item column3 'something';

The basic abstraction of SQL is a table with multiple columns, and each column contains a value and has his own name; the value of a given column can be extracted by matching the value of known other columns within the same row.

The basic abstraction of SPARQL is a single table with only three columns subject, predicate and object, and rows with the same subject belongs to the same entity; using multiple combinations of triples (subject + predicate + object), where each element can be a parameter (the tokens starting with ?) having to eventually match in other triples where it appears, you can retrieve the required information.

SPARQLer permits to create SPARQL queries in a more "SQL-like" fashion, introducing a few implicit behavours (that can be overridden, if required, with certain functions and combinations of parameters).

$client->doSelect(['column1', 'column2'])->where('column3', 'something')->get();

Where not otherwise explicited, the subject part of the SPARQL query is implicit: the selected attributes and all attributes used in the conditions refer to the same value.

For some example of actual SPARQL queries, in raw format and rewrote with SPARQLer, get a look to the examples page.

Glossary

A few definitions useful to understand the SPARQLer API applied to the SPARQL model.

Client is the object which provides the connection to the SPARQL endpoint. This includes the API to init a Builder
Builder is the object used to compose and execute the actual query, as a concatenation of conditions and filters
Ontology is the description of available Predicates within a given semantic context. Each ontology may refer to other ontologies, and the data into a SPARQL model usually include multiple ontologies. The name of an Ontology is an URL, more often rappresented with a prefix
Namespace is the prefix used to short the name of Predicates included into a given Ontology. http://xmlns.com/foaf/0.1/mbox is the same of foaf:mbox
Term is a single token into the query; there are many Term types, each providing a specific meaning and altering the behavior of the Triple in which appear and/or of the whole query.
Triple is a set of three Term: the first is the subject the second is predicate and the third is object. In the SPARQLer public API those are rappresented just as arrays, if a minor number of elements is provided (usually 2, sometime 1) the missing ones are filled implicitely
Subject is a string, often an URL, that aggregates multiple Triple. In the SPARQL data model, all triples having the same subject belong to the same entity. In a SPARQLer query, this information is held into a OwnSubject term
Predicate is the name of a single attribute in an entity: usually is an URL, or may be in "short" form using the prefix of the Namespace (e.g. foaf:mbox). In a SPARQLer query, those are wrapped into a Iri term (which may also rappresent the Subject of a specific entity)
Object is the value for a given attribute. Often it is rappresented as a Literal
Result is the object containing the product of a SELECT query: can be iterated and each element is an associative array in the form predicate => value
Literal is an object usually used to enclose a value (a string, a number, a date...) and his own datatype. Leveraging EasyRDF's TypeMapper it is possible to automatically convert those values in structured objects
Graph is a collection of Resource, usually returned by a CONSTRUCT query
Resource rappresents a single entity, having his own Subject and his own properties
Model is a representation or a Resource of a given type, which implementation can be customized and extended to better integrate within your application