The implementation of metalevels in ERP5 is based on an extension of the concept of "topic" in the Zope CMF

Global classification

A global classification is defined as a forrest of trees.

Each tree represents a classification hierarchy. For example

europe

europe/france

europe/germany

americas

americas/unitedstates

or for example:

mailorder

mailorder/internet

retailer

whosale

Each object in ERP5 can be associated to one or more leafs of each tree of the classification forrest.

Topics

Topics are objects which allow to list a certain number of objects which satisfy a certain number of criteria. In ERP5, most criteria are implemented as SQL requests. Criteria include

• membership of an object to a leaf of a classification tree
• value of an attribute of an object

Topics can be used in order to find all objects which satisfy a given set of critereria.

Objects listed in a topic may be of any class.

Subtopics

Topics can contain other topics in order to form a navigable chain of topics. Subtopics can acquire constraints of a topic.

Attribute Aggregation

Besides criteria, topics may include the possibility of achieving aggregations of attributes for all objects of given list of types (ex. all objects which are instance of a movement or a subclass or movement).

Aggregations may be defined as objects inside a topic or at the top level.

Aggregations may for example contain the following attributes

• a list of classes which may belong to an aggregation
• a list of attributes to consider
• a list of aggregation functions
• a list of attributes to sort on

Metanodes

Metanodes are defined as objects which are stored at the topic level.

A metanode acquires its topic criteria and behaves like a node.

Metaresources

Metaresourecs are defined as objects are stored at the topic level.

A metaresource acquires its topic criteria and behaves like a node.