cybertools/relation/interfaces.py

#
#  Copyright (c) 2020 Helmut Merz helmutm@cy55.de
#
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#  GNU General Public License for more details.
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"""
interface definitions for the Relations utility and relation objects.
"""

from zope.interface import Interface, Attribute
from zope.interface.interfaces import IObjectEvent


# relation interfaces

class IRelation(Interface):
    """ Base interface for relations.
    """

    order = Attribute('An integer that may be used for ordering relations. '
                'The default should be 0, and there may be negative and '
                'positive values.')
    relevance = Attribute('A float greater than 0.0 and less or equal to '
                '1.0 denoting the importance, relevance, or weight of a '
                'relation. The default and standard value should be 1.0.')

    def getPredicateName():
        """ Return the predicate of this relation as a string that may be
            used for indexing.
        """

    def validate(registry=None):
        """ Return True if this relation is valid.

            If the registry argument is provided the check should be done
            with respect to this relation registry. The validate() method
            may be used for implementing checks against ontologies or other
            kinds of restrictions.
        """


class IMonadicRelation(IRelation):
    """ Relation with just one object.

        While a monadic relation could be easily represented by an attribute
        or an annotation, monadic relations are e.g. useful when working with
        an ontology-driven higher-level relation framework.
    """

    first = Attribute('First and only object that belongs to the relation.')


class IDyadicRelation(IRelation):
    """ Relation connecting two objects.
    """

    first = Attribute('First object that belongs to the relation.')
    second = Attribute('Second object that belongs to the relation.')


class ITriadicRelation(IDyadicRelation):
    """ Relation connecting three objects.
    """

    third = Attribute('Third object that belongs to the relation.')


# this is just a conceptual try - thinking about storing
# relations as attributes...
class IAttributeRelation(IDyadicRelation):
    """ A type of relation that will be stored in attributes of the
        objects that take part in the relation. You have to use a
        relation registry that provides IAttributeRelationRegistry
        for registering/managing relations of this type.
    """

    attributeNameFirst = Attribute('Name of the attribute in which the '
                        'relation will be stored on the `first` object. '
                        'Typically a class attribute.')
    attributeNameSecond = Attribute('Name of the attribute in which the '
                        'relation will be stored on the `second` object.'
                        'Typically a class attribute.')


class IPredicate(Interface):
    """ A predicate signifies a relationship. This may be implemented
        directly as a relation class, or the relation object may
        hold the predicate as an attribute.
    """

    def getPredicateName():
        """ Return this predicate as a string that may be used for indexing.
        """


# event interfaces

class IRelationInvalidatedEvent(IObjectEvent):
    """ This event fires when a relation is invalidated, typically because
        an object that is involved in the relation is removed.
    """


# marker interfaces

class IRelatable(Interface):
    """ Marker interface for objects that may have relations associated
        with them. Should be checked by IRelationRegistry.register()
        and event handlers.
    """


# relation registry interfaces

class IRelationRegistryUpdate(Interface):
    """ Interface for registering and unregistering relations with a
        relation registry.
    """

    def register(relation):
        """ Register the relation given with this registry.
        """

    def unregister(relation):
        """ Remove the relation given from this registry.
        """

    def getUniqueIdForObject(object):
        """ Return an identifier for the object given that is unique at
            least within the scope of this registry.
        """


class IRelationRegistryQuery(Interface):
    """ Interface for querying a relation registry.
    """

    def query(example=None, **kw):
        """ Return a sequence of relations that fulfill the criteria given.

            You may provide a relation object as an example that specifies the
            search criteria, i.e. its predicate and first, second or third
            attribute will be used for searching, or explicit criteria
            via keyword arguments.

            Example for using keyword criteria:
                rr.queryRelations(first=someObject, second=anotherObject,
                                  relationship=SomeRelationClass)
        """


class IRelationRegistry(IRelationRegistryUpdate, IRelationRegistryQuery):
    """ A registry for registering and searching relations typically
        implemented as a local utility .
    """