# HG changeset patch
# User Sandrine Ribeau <sandrine.ribeau@logilab.fr>
# Date 1228951440 28800
# Wed Dec 10 15:24:00 2008 -0800
# Node ID 8ea90dc15b76a5bc5d34f0e443cfa7fd5735a674
# Parent 242b229a9d96e9423325c711170a5754ba187256
[doc] Initial englaish translation of RQL specs.
diff --git a/doc/specifications_en.txt b/doc/specifications_en.txt
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+.. -*- coding: utf-8 -*-
+
+
+===================================================
+Specification "Relations Query Language" (Hercules)
+===================================================
+
+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`
+scheam 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.
+
+See also
+``````````
+RDFQL_
+
+
+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.
+
+
+
+Examples
+========
+
+(see the tutorial: ref: `tutorielRQL` for more examples)
+
+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*
+ ::
+
+ Person P WHERE
+ P work_for P, S name 'Eurocopter'
+ P interested_by T, T name 'training'
+
+- *Search note less than 10 days old written by jphc or ocy*
+ ::
+
+ Note N WHERE
+ N written_on D, D day> (today -10),
+ N written_by P, P name 'jphc' or P name 'ocy'
+
+- *Looking for people interested in training or living in Paris*
+ ::
+
+ Person P WHERE
+ (P interested_by T, T name 'training') or
+ (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 Person X: X name 'widget'
+
+- *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,
+ WHERE, AND, OR, NOT
+ IN, LIKE,
+ TRUE, FALSE, NULL, TODAY, NOW
+ GROUPBY, ORDERBY, ASC, DESC
+
+
+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.
+
+Base 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
+``````````````````
+
+- For grouped queries (e.g. with a GROUPBY clause), all
+ selected variables should be grouped.
+
+- To group and/or sort by attributes, we can do: "X,L user U, U
+ login L GROUPBY L, X ORDERBY L"
+
+- If the sorting method (SORT_METHOD) is not specified, then the sorting is
+ ascendant.
+
+Negation
+````````
+
+* A query such as `Document X WHERE NOT X owned_by U` means "the
+ documents have no relation `owned_by`".
+* But the query `Document X WHERE NOT X owned_by U, U login "syt"`
+ means "the documents have no relation `owned_by` with the user
+ syt". They may have a relation "owned_by" with another user.
+
+Identity
+````````
+
+You can use the special relation `identity` in a query to
+add an identity constraint between two variables. This is equivalent
+to ``is`` in python::
+
+ Any A WHERE A comments B, A identity B
+
+return all objects that comment themselves. The relation
+`identity` is especially useful when defining the rules for securities
+with `RQLExpressions`.
+
+Implementation
+==============
+
+Internal representation (syntactic tree)
+----------------------------------------
+
+The tree research does not contain the selected variables
+(e.g. there is only what follows "WHERE").
+
+The insertion tree does not contain the variables inserted or relations
+defined on these variables (e.g. there is only what follows "WHERE").
+
+The removal tree does not contain the deleted variables and relations
+(e.g. there is only what follows the "WHERE").
+
+The update tree does not contain the variables and relations updated
+(e.g. there is only what follows the "WHERE").
+
+::
+
+ Select ((Relationship | And | Gold)?, Group?, Sort?)
+ Insert (Relations | And | Gold)?
+ Delete (Relationship | And | Gold)?
+ Update (Relations | And | Gold)?
+
+ And ((Relationship | And | Gold), (Relationship | And | Gold))
+ Or ((Relationship | And | Gold), (Relationship | And | Gold))
+
+ Relationship ((VariableRef, Comparison))
+
+ Comparison ((Function | MathExpression | Keyword | Constant | VariableRef) +)
+
+ Function (())
+ MathExpression ((MathExpression | Keyword | Constant | VariableRef), (MathExpression | Keyword | Constant | VariableRef))
+
+ Group (VariableRef +)
+ Sort (SortTerm +)
+ SortTerm (VariableRef +)
+
+ VariableRef ()
+ Variable ()
+ Keyword ()
+ Constant ()
+
+
+Remarks
+-------
+
+- The current implementation does not support linking two relations of type
+ 'is' with a OR. I do not think that the negation is supported on this type
+ of relation (XXX FIXME to be confirmed).
+
+- Relations defining the variables must be left to those using them.
+ For example::
+
+ Point P where P abs X, P ord Y, P value X+Y
+
+ is valid, but::
+
+ Point P where P abs X, P value X+Y, P ord Y
+
+ is not.
+
+
+
+Conclusion
+==========
+
+Limitations
+-----------
+
+It lacks at the moment:
+
+- COALESCE
+
+- restrictions on groups (HAVING)
+
+and certainly other things ...
+
+A disadvantage is that to use this language we must know the
+format used (with real relation names and entities, not those viewing
+in the user interface). On the other hand, we can not really bypass
+that, and it is the job of a user interface to hide the RQL.
+
+
+Topics
+------
+
+It would be convenient to express the schema matching
+relations (non-recursive rules)::
+
+ Document class Type <-> Document occurence_of Fiche class Type
+ Sheet class Type <-> Form collection Collection class Type
+
+Therefore 1. becomes::
+
+ Document X where
+ X class C, C name 'Cartoon'
+ X owned_by U, U login 'syt'
+ X available true
+
+I'm not sure that we should handle this at RQL level ...
+
+There should also be a special relation 'anonymous'.
+
+
+
+.. _Versa: Http://uche.ogbuji.net/tech/rdf/versa/
+.. _RDFQL: Http://www.w3.org/TandS/QL/QL98/pp/rdfquery.html
+