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+Introduction
+------------
+
+Goals of RQL
+~~~~~~~~~~~~
+
+The goal is to have a language emphasizing the way of browsing
+relations. As such, attributes will be regarded as cases of
+special relations (in terms of implementation, the language
+user should see virtually no difference between an attribute and a
+relation).
+
+RQL is inspired by SQL but is the highest level. A knowledge of the 
+`CubicWeb` schema defining the application is necessary.
+
+Comparison with existing languages
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+SQL
+```
+RQL builds on the features of SQL but is at a higher level
+(the current implementation of RQL generates SQL). For that it is limited
+to the way of browsing relations and introduces variables. 
+The user does not need to know the model underlying SQL, but the `CubicWeb` 
+schema defining the application.
+
+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 is some
+number of 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 may need to be guided at one time or another. 
+Finally, the syntax is a little esoteric.
+
+Sparql
+``````
+The query language most similar to RQL is SPARQL_, defined by the W3C to serve
+for the semantic web. 
+
+
+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/