.. _rql_intro:

Introduction
------------

Goals of RQL
~~~~~~~~~~~~

The goal is to have a language making relations browsing easy. As
such, attributes will be regarded as cases of special relations (in
terms of usage, the user should see no syntactic difference between an
attribute and a relation).

Comparison with existing languages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SQL
```

RQL may remind of SQL but works at a higher abstraction level (the *CubicWeb*
framework generates SQL from RQL to fetch data from relation databases). RQL is
focused on browsing relations. The user needs only to know about the *CubicWeb*
data model he is querying, but not about the underlying SQL model.

Sparql
``````

The query language most similar to RQL is SPARQL_, defined by the W3C to serve
for the semantic web.

Versa
`````

We should look in more detail, but here are already some ideas for the moment
... Versa_ is the language most similar to what we wanted to do, but the model
underlying data being RDF, there are some things such as namespaces or
handling of the RDF types which does not interest us. On the functionality
level, Versa_ is very comprehensive including through many functions of
conversion and basic types manipulation, which we may want to look at one time
or another.  Finally, the syntax is a little esoteric.


The different types of queries
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Search (`Any`)
   Extract entities and attributes of entities.

Insert entities (`INSERT`)
   Insert new entities or relations in the database.
   It can also directly create relationships for the newly created entities.

Update entities, create relations (`SET`)
   Update existing entities in the database,
   or create relations between existing entities.

Delete entities or relationship (`DELETE`)
   Remove entities or relations existing in the database.




.. _Versa: http://uche.ogbuji.net/tech/rdf/versa/
.. _SPARQL: http://www.w3.org/TR/rdf-sparql-query/