.. -*- coding: utf-8 -*-

.. _RQL:

======================================

RQL language (Relation Query Language)

======================================

Introduction

============

Goals 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 user

language not to 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

`````

Should I look in more detail, but here is 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`)

   This type of query can extract entities and attributes of entities.

Inserting entities (`INSERT`)

   This type of query is used to insert new entities in the database. It

   will also create direct relationships entities newly created.

Update entities, relations creation (`SET`)

   This type of query updates existing entities in the database,

   or create relations between existing entities.

Deletion of entities or relationship (`DELETE`)

   This type of query allows for the removal of entities and relations existing

   in the database.

Search Query

------------

   [ `DISTINCT`] <entity type> V1 (V2) \ *

   [ `GROUPBY` V1 (V2) \*] [ `ORDERBY` <orderterms>]

   [ `WHERE` <restriction>]

   [ `LIMIT` <value>] [ `OFFSET` <value>]

:entity type:

   Type of selected variables.

   The special type `Any` is equivalent to not specify a type.

:restriction:

   list of relations to go through whic follow the pattern

     `V1 relation V2 | <static value>`

:orderterms:

   Definition of the selection order: variable or column number followed by

   sorting method ( `ASC`, `DESC`), ASC is the default.

:note for grouped queries:

   For grouped queries (e.g., a clause `GROUPBY`), all

   selected variables must be aggregated or grouped.

- *Search for the object of identifier 53*

   ::

        Any WHERE X

        X eid 53

- *Search material such as comics, owned by syt and available*

   ::

        WHERE X Document

        X occurence_of F, F class C, C name 'Comics'

        X owned_by U, U login 'syt'

        X available true

- *Looking for people working for eurocopter interested in training*

   ::

        P interested_by T, T name 'training'

- *Search note less than 10 days old written by jphc or ocy*

   ::

        N written_by P, P name 'jphc' or P name 'ocy'

- *Looking for people interested in training or living in Paris*

   ::

        (P city 'Paris')

- *The name and surname of all people*

   ::

        Any N, P WHERE

        X is Person, X name N, X first_name P

   Note that the selection of several entities generally force

   the use of "Any" because the type specification applies otherwise

   to all the selected variables. We could write here

   ::

        String N, P WHERE

        X is Person, X name N, X first_name P

Insertion query

---------------

    `INSERT` <entity type> V1 (, <entity type> V2) \ * `:` <assignments>

    [ `WHERE` <restriction>]

: assignments:

   list of relations to assign in the form `V1 relationship V2 | <static value>`

The restriction can define variables used in assignments.

Caution, if a restriction is specified, the insertion is done for 

*each line results returned by the restriction*.

- *Insert a new person named 'foo'*

   ::

- *Insert a new person named 'foo', another called 'nice' and a 'friend' relation

  between them*

  ::

        INSERT Person X, Person Y: X name 'foo', Y name 'nice', X friend Y

- *Insert a new person named 'foo' and a 'friend' relation with an existing 

  person called 'nice'*

  ::

        INSERT Person X: X name 'foo', X friend  Y WHERE name 'nice'

Update and relation creation queries

------------------------------------

    `SET` <assignements>

    [ `WHERE` <restriction>]

Caution, if a restriction is specified, the update is done *for

each line results returned by the restriction*.

- *Renaming of the person named 'foo' to 'bar' with the first name changed*

  ::

        SET X name 'bar', X first_name 'original' where X is Person X name 'foo'

- *Insert a relation of type 'know' between objects linked by 

  the relation of type 'friend'*

  ::

        SET X know Y  WHERE X friend Y

Deletion query

--------------

    `DELETE` (<entity type> V) | (V1 relation v2 ),...

    [ `WHERE` <restriction>]

Caution, if a restriction is specified, the deletion is made *for

each line results returned by the restriction*.

- *Deletion of the person named 'foo'*

  ::

        DELETE Person X WHERE X name 'foo'

- *Removal of all relations of type 'friend' from the person named 'foo'*

  ::

        DELETE X friend Y WHERE X is Person, X name 'foo'

Language definition

===================

Reserved keywords

-----------------

The keywords are not case sensitive.

::

     DISTINCT, INSERT, SET, DELETE,

Variables and Typing

--------------------

With RQL, we do not distinguish between entities and attributes. The

value of an attribute is considered an entity of a particular type (see

below), linked to one (real) entity by a relation called the name of

the attribute.

Entities and values to browse and/or select are represented in

the query by *variables* that must be written in capital letters.

There is a special type **Any**, referring to a non specific type.

We can restrict the possible types for a variable using the

special relation **is**.

The possible type(s) for each variable is derived from the schema

according to the constraints expressed above and thanks to the relations between

each variable.

Built-in types

``````````````

The base types supported are string (between double or single quotes),

integers or floats (the separator is the'.'), dates and

boolean. We expect to receive a schema in which types String,

Int, Float, Date and Boolean are defined.

* `String` (literal: between double or single quotes).

* `Int`, `Float` (separator being'.').

* `Date`, `Datetime`, `Time` (literal: string YYYY/MM/DD [hh:mm] or keywords

   `TODAY` and `NOW`).

* `Boolean` (keywords `TRUE` and `FALSE`).

* `Keyword` NULL.

Operators

---------

Logical Operators

```````````````````

::

     AND, OR, ','

',' is equivalent to 'AND' but with the smallest among the priority

of logical operators (see :ref:`PriorityOperators`).

Mathematical Operators

``````````````````````

::

     +, -, *, /

Comparison operators

````````````````````

::

     =, <, <=, >=, > = ~, IN, LIKE

* The operator `=` is the default operator.

* The operator `LIKE` equivalent to `~=` can be used with the

  special character `%` in a string to indicate that the chain 

  must start or finish by a prefix/suffix:

  ::

     Any X WHERE X name =~ 'Th%'

     Any X WHERE X name LIKE '%lt'

* The operator `IN` provides a list of possible values:

  ::

    Any X WHERE X name IN ( 'chauvat', 'fayolle', 'di mascio', 'thenault')

XXX nico: A trick <> 'bar' would not it be more convenient than NOT A

trick 'bar'?

.. _PriorityOperators:

Operators priority

``````````````````

1. '*', '/'

2. '+', '-'

3. 'and'

4. 'or'

5. ','

Advanced Features

-----------------

Functions aggregates

````````````````````

::

     COUNT, MIN, MAX, AVG, SUM

Functions on string

```````````````````

::

     UPPER, LOWER

Optional relations

``````````````````

* They allow you to select entities related or not to another.

* You must use the `?` behind the variable to specify that the relation

  toward it is optional:

   - Anomalies of a project attached or not to a version ::

       Any X, V WHERE X concerns P, P eid 42, X corrected_in V?

   - All cards and the project they document if necessary ::

       Any C, P WHERE C is Card, P? documented_by C

BNF grammar

-----------

The terminal elements are in capital letters, non-terminal in lowercase.

The value of the terminal elements (between quotes) is a Python regular

expression.

::

     statement:: = (select | delete | insert | update) ';'

     # select specific rules

     select      ::= 'DISTINCT'? E_TYPE selected_terms restriction? group? sort?

     selected_terms ::= expression ( ',' expression)*

     group       ::= 'GROUPBY' VARIABLE ( ',' VARIABLE)*

     sort        ::= 'ORDERBY' sort_term ( ',' sort_term)*

     sort_term   ::=  VARIABLE sort_method =?

     sort_method ::= 'ASC' | 'DESC'

     # delete specific rules

     delete ::= 'DELETE' (variables_declaration | relations_declaration) restriction?

     # insert specific rules

     insert ::= 'INSERT' variables_declaration ( ':' relations_declaration)? restriction?

     # update specific rules

     update ::= 'SET' relations_declaration restriction

     # common rules

     variables_declaration ::= E_TYPE VARIABLE (',' E_TYPE VARIABLE)*

     relations_declaration ::= simple_relation (',' simple_relation)*

     simple_relation ::= VARIABLE R_TYPE expression

     restriction ::= 'WHERE' relations

     relations   ::= relation (LOGIC_OP relation)*

                   | '(' relations')'

     relation    ::= 'NOT'? VARIABLE R_TYPE COMP_OP? expression

                   | 'NOT'? R_TYPE VARIABLE 'IN' '(' expression (',' expression)* ')'

     expression  ::= var_or_func_or_const (MATH_OP var_or_func_or_const) *

                   | '(' expression ')'

     var_or_func_or_const ::= VARIABLE | function | constant

     function    ::= FUNCTION '(' expression ( ',' expression) * ')'

     constant    ::= KEYWORD | STRING | FLOAT | INT

     # tokens

     LOGIC_OP ::= ',' | 'GOLD' | 'AND'

     MATH_OP  ::= '+' | '-' | '/' | '*'

     COMP_OP  ::= '>' | '>=' | '=' | '<=' | '<' | '~=' | 'LIKE'

     FUNCTION ::= 'MIN' | 'MAX' | 'SUM' | 'AVG' | 'COUNT' | 'upper' | 'LOWER'

     VARIABLE ::= '[A-Z][A-Z0-9]*'

     E_TYPE   ::= '[A-Z]\w*'

     R_TYPE   ::= '[a-z_]+'

     KEYWORD  ::= 'TRUE' | 'FALSE' | 'NULL' | 'TODAY' | 'NOW'

     STRING   ::= "'([^'\]|\\.)*'" |'"([^\"]|\\.)*\"'

     FLOAT    ::= '\d+\.\d*'

     INT      ::= '\d+'

Remarks

-------

Sorting and groups