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+++ b/doc/book/en/03-sect-definition-schema.en.txt Fri Nov 14 11:05:32 2008 +0100
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+.. -*- coding: utf-8 -*-
+
+Entity type definition
+----------------------
+
+An entity type is defined by a Python class which inherits `EntityType`. The
+class name correponds to the type name. Then the content of the class contains
+the description of attributes and relations for the defined entity type,
+by example ::
+
+ class Personne(EntityType):
+ """A person with the properties and the relations necessarry for my
+ application"""
+
+ last_name = String(required=True, fulltextindexed=True)
+ first_name = String(required=True, fulltextindexed=True)
+ title = String(vocabulary=('M', 'Mme', 'Mlle'))
+ date_of_birth = Date()
+ works_for = SubjectRelation('Company', cardinality='?*')
+
+* the name of the Python attribute corresponds to the name of the attribute
+ or the relation in `LAX` application.
+
+* all built-in types are available : `String`, `Int`, `Float`,
+ `Boolean`, `Date`, `Datetime`, `Time`, `Byte`.
+
+* each entity has at least the following meta-relations :
+
+ - `eid` (`Int`)
+
+ - `creation_date` (`Datetime`)
+
+ - `modification_date` (`Datetime`)
+
+ - `created_by` (`EUser`) (which user created the entity)
+
+ - `owned_by` (`EUser`) (who does the entity belongs to, by default the
+ creator but not necessarry and it could have multiple owners)
+
+ - `is` (`EEType`)
+
+
+* it is also possible to define relations of type object by using `ObjectRelation`
+ instead of `SubjectRelation`
+
+* the first argument of `SubjectRelation` and `ObjectRelation` gives respectively
+ the object/subject entity type of the relation. This could be :
+
+ * a string corresponding to an entity type
+
+ * a tuple of string correponding to multiple entities types
+
+ * special string such as follows :
+
+ - "**" : all types of entities
+ - "*" : all types of entities non meta
+ - "@" : all types of meta entities but not system entities (e.g. used for
+ the basis schema description)
+
+* it is possible to use the attribute `meta` to flag an entity type as a `meta`
+ (e.g. used to describe/categorize other entities)
+
+* optional properties for attributes and relations :
+
+ - `description` : string describing an attribute or a relation. By default
+ this string will be used in the editing form of the entity, which means
+ that it is supposed to help the end-user and should be flagged by the
+ function `_` to be properly internationalized.
+
+ - `constraints` : list of conditions/constraints that the relation needs to
+ satisfy (c.f. `Contraints`_)
+
+ - `cardinality` : two characters string which specify the cardinality of the
+ relation. The first character defines the cardinality of the relation on
+ the subject, the second on the object of the relation. When a relation
+ has multiple possible subjects or objects, the cardinality applies to all
+ and not on a one to one basis (so it must be consistent...). The possible
+ values are inspired from regular expressions syntax :
+
+ * `1`: 1..1
+ * `?`: 0..1
+ * `+`: 1..n
+ * `*`: 0..n
+
+ - `meta` : boolean indicating that the relation is a meta-relation (false by
+ default)
+
+* optionnal properties for attributes :
+
+ - `required` : boolean indicating if the attribute is required (false by default)
+
+ - `unique` : boolean indicating if the value of the attribute has to be unique
+ or not within all entities of the same type (false by default)
+
+ - `indexed` : boolean indicating if an index needs to be created for this
+ attribute in the database (false by default). This is usefull only if
+ you know that you will have to run numerous searches on the value of this
+ attribute.
+
+ - `default` : default value of the attribute. In case of date types, the values
+ which could be used correpond to the RQL keywords `TODAY` and `NOW`.
+
+ - `vocabulary` : specify static possible values of an attribute
+
+* optionnal properties of type `String` :
+
+ - `fulltextindexed` : boolean indicating if the attribute is part of
+ the full text index (false by default) (*applicable on the type `Byte`
+ as well*)
+
+ - `internationalizable` : boolean indicating if the value of the attribute
+ is internationalizable (false by default)
+
+ - `maxsize` : integer providing the maximum size of the string (no limit by default)
+
+* optionnal properties for relations :
+
+ - `composite` : string indicating that the subject (composite == 'subject')
+ is composed of the objects of the relations. For the opposite case (when
+ the object is composed of the subjects of the relation), we just need
+ to set 'object' as the value. The composition implies that when the relation
+ is deleted (so when the composite is deleted), the composed are also deleted.
+ [PAS CLAIR]
+
+Contraints
+``````````
+By default, the available constraints types are :
+
+* `SizeConstraint` : allows to specify a minimum and/or maximum size on
+ string (generic case of `maxsize`)
+
+* `BoundConstraint` : allows to specify a minimum and/or maximum value on
+ numeric types
+
+* `UniqueConstraint` : identical to "unique=True"
+
+* `StaticVocabularyConstraint` : identical to "vocabulary=(...)"
+
+* `RQLConstraint` : allows to specify a RQL query that needs to be satisfied
+ by the subject and/or the object of the relation. In this query the variables
+ `S` and `O` are reserved for the entities subject and object of the
+ relation.
+
+* `RQLVocabularyConstraint` : similar to the previous type of constraint except
+ that it does not express a "strong" constraint, which means it is only used to
+ restrict the values listed in the drop-down menu of editing form, but it does
+ not prevent another entity to be selected
+ [PAS CLAIR]
+
+
+Relation type definition
+------------------------
+
+A relation is defined by a Python class heriting `RelationType`. The name
+of the class corresponds to the name of the type. The class then contains
+a description of the properties of this type of relation, as well as a
+string for the subject and a string for the object. This allows to create
+new definition of associated relations, (so that the class can have the
+definition properties from the relation)[PAS CLAIR] by example ::
+
+ class locked_by(RelationType):
+ """relation on all entities indicating that they are locked"""
+ inlined = True
+ cardinality = '?*'
+ subject = '*'
+ object = 'EUser'
+
+In addition to the permissions, the own properties of the relation types
+(shared also by all definition of relation of this type) are :
+
+
+* `inlined` : boolean handling the physical optimization for archiving
+ the relation in the subject entity table, instead of creating a specific
+ table for the relation. This applies to the relation when the cardinality
+ of subject->relation->object is 0..1 ('?') or 1..1 ('1')
+
+* `symetric` : boolean indication that the relation is symetrical, which
+ means `X relation Y` implies `Y relation X`
+
+In the case of simultaneous relations definitions, `subject` and `object`
+can both be equal to the value of the first argument of `SubjectRelation`
+and `ObjectRelation`.
+
+When a relation is not inlined and not symetrical, and it does not require
+specific permissions, its definition (by using `SubjectRelation` and
+`ObjectRelation`) is all we need.
+
+Permissions definition
+----------------------
+
+Define permissions is set through to the attribute `permissions` of entities and
+relations types. It defines a dictionnary where the keys are the access types
+(action), and the values are the authorized groups or expressions.
+
+For an entity type, the possible actions are `read`, `add`, `update` and
+`delete`.
+
+For a relation type, the possible actions are `read`, `add`, and `delete`.
+
+For each access type, a tuple indicates the name of the authorized groups and/or
+one or multiple RQL expressions to satisfy to grant access. The access is
+provided once the user is in the listed groups or one of the RQL condition is
+satisfied.
+
+The standard groups are :
+
+* `guests`
+
+* `users`
+
+* `managers`
+
+* `owners` : virtual group corresponding to the entity's owner.
+ This can only be used for the actions `update` and `delete` of an entity
+ type.
+
+It is also possible to use specific groups if they are define in the precreate
+of the application (``migration/precreate.py``).
+
+Use of RQL expression for writing rights
+````````````````````````````````````````
+It is possible to define RQL expression to provide update permission
+(`add`, `delete` and `update`) on relation and entity types.
+
+RQL expression for entity type permission :
+
+* you have to use the class `ERQLExpression`
+
+* the used expression corresponds to the WHERE statement of an RQL query
+
+* in this expression, the variables X and U are pre-defined references
+ respectively on the current entity (on which the action is verified) and
+ on the user who send the request
+
+* it is possible to use, in this expression, a special relation
+ "has_<ACTION>_permission" where the subject is the user and the
+ object is a any variable, meaning that the user needs to have
+ permission to execute the action <ACTION> on the entities related
+ to this variable
+
+For RQL expressions on a relation type, the principles are the same except
+for the following :
+
+* you have to use the class `RQLExpression` in the case of a non-final relation
+ [WHAT IS A NON FINALE RELATION]
+
+* in the expression, the variables S, O and U are pre-defined references
+ to respectively the subject and the object of the current relation (on
+ which the action is being verified) and the user who executed the query
+
+* we can also defined rights on attributes of an entity (non-final relation),
+ knowing that :
+
+ - to defines RQL expression, we have to use the class `ERQLExpression`
+ in which X represents the entity the attribute belongs to
+
+ - the permissions `add` and `delete` are equivalent. Only `add`/`read`
+ are actually taken in consideration.
+
+
+
+In addition to thatm the entity type `EPermission` from the standard library
+allow to build very complex and dynamic security architecture. The schema of
+this entity type is as follow : ::
+
+ class EPermission(MetaEntityType):
+ """entity type that may be used to construct some advanced security configuration
+ """
+ name = String(required=True, indexed=True, internationalizable=True, maxsize=100)
+ require_group = SubjectRelation('EGroup', cardinality='+*',
+ description=_('groups to which the permission is granted'))
+ require_state = SubjectRelation('State',
+ description=_("entity'state in which the permission is applyable"))
+ # can be used on any entity
+ require_permission = ObjectRelation('**', cardinality='*1', composite='subject',
+ description=_("link a permission to the entity. This "
+ "permission should be used in the security "
+ "definition of the entity's type to be useful."))
+
+
+Example of configuration ::
+
+ ...
+
+ class Version(EntityType):
+ """a version is defining the content of a particular project's release"""
+
+ permissions = {'read': ('managers', 'users', 'guests',),
+ 'update': ('managers', 'logilab', 'owners',),
+ 'delete': ('managers', ),
+ 'add': ('managers', 'logilab',
+ ERQLExpression('X version_of PROJ, U in_group G,'
+ 'PROJ require_permission P, P name "add_version",'
+ 'P require_group G'),)}
+
+ ...
+
+ class version_of(RelationType):
+ """link a version to its project. A version is necessarily linked to one and only one project.
+ """
+ permissions = {'read': ('managers', 'users', 'guests',),
+ 'delete': ('managers', ),
+ 'add': ('managers', 'logilab',
+ RRQLExpression('O require_permission P, P name "add_version",'
+ 'U in_group G, P require_group G'),)
+ }
+ inlined = True
+
+This configuration assumes/indicates [???] that an entity `EPermission` named
+"add_version" can be associated to a project and provides rights to create
+new versions on this project to specific groups. It is important to notice that :
+
+* in such case, we have to protect both the entity type "Version" and the relation
+ associating a version to a project ("version_of")
+
+* because of the genricity of the entity type `EPermission`, we have to execute
+ a unification with the groups and/or the states if necessary in the expression
+ ("U in_group G, P require_group G" in the above example)
+
+
+Use of RQL expression for reading rights
+````````````````````````````````````````
+
+The principles are the same but with the following restrictions :
+
+* we can not [??] `RRQLExpression` on relation types for reading
+
+* special relations "has_<ACTION>_permission" can not be used
+
+
+Note on the use of RQL expression for `add` permission
+``````````````````````````````````````````````````````
+Potentially, the use of an RQL expression to add an entity or a relation
+can cause problems for the user interface, because if the expression uses
+the entity or the relation to create, then we are not able to verify the
+permissions before we actually add the entity (please note that this is
+not a problem for the RQL server at all, because the permissions checks are
+done after the creation). In such case, the permission checks methods
+(check_perm, has_perm) can indicate that the user is not allowed to create
+this entity but can obtain the permission.
+To compensate this problem, it is usually necessary, for such case,
+to use an action that reflects the schema permissions but which enables
+to check properly the permissions so that it would show up if necessary.
+[PAS CLAIR]