a representation of the organization of records and is not an exact representation of entities and relationships." Several other authors also support Chen's program: Philosophical alignment Chen is in accord with philosophical traditions from the time of the Ancient Greek philosophers: Plato and Aristotle. Plato himself associates knowledge with the apprehension of unchanging Forms (namely, archetypes or abstract representations of the many types of things, and properties) and their relationships to one another. Limitations An ER model is primarily conceptual, an ontology that expresses predicates in a domain of knowledge. ER models are readily used to represent relational database structures (after Codd and Date) but not so often to represent other kinds of data structure (data warehouses, document stores etc.) Some ER model notations include symbols to show super-sub-type relationships and mutual exclusion between relationships; some don't. An ER model does not show an entity's life history (how its attributes and/or relationships change over time in response to events). For many systems, such state changes are nontrivial and important enough to warrant explicit specification. Some have extended ER modeling with constructs to represent state changes, an approach supported by the original author; an example is Anchor Modeling. Others model state changes separately, using state transition diagrams or some other process modeling technique. Many other kinds of diagram are drawn to model other aspects of systems, including the 14 diagram types offered by UML. Today, even where ER modeling could be useful, it is uncommon because many use tools that support similar kinds of model, notably class diagrams for OO programming and data models for relational database management systems. Some of these tools can generate code from diagrams and reverse-engineer diagrams from code. In a survey, Brodie and Liu could not find a single instance of entity–relationship modeling inside a sample of ten Fortune 100 companies. Badia and Lemire blame this lack of use on the lack of guidance but also on the lack of benefits, such as lack of support for data integration. The enhanced entity–relationship model (EER modeling) introduces several concepts not in ER modeling, but are closely related to object-oriented design, like is-a relationships. For modelling temporal databases, numerous ER extensions have been considered. Similarly, the ER model was found unsuitable for multidimensional databases (used in OLAP applications); no dominant conceptual model has emerged in this field yet, although they generally revolve around the concept of OLAP cube