I am not proficient in the original concept of ER diagram, but in CDM, there are three other properties that can be set: mandatory (mandatory contact), dependent (dependency contact/demarcation Association), and dominant (controlled connection). When we mention the relationship between entities, the first thing I'm afraid of is one to One,one to many and many to many the three types of contact, these contact types are most familiar to you.

'See, maybe the concept of connection is really too simple, so instead of that Well, so the documentation for PD is also an example of what happens when we think that there is a connection between the two entities. This relationship expresses the all employee works in a team and the each team have employees.

For example, with a CDM that manages human resources, the relationship Member links the entities Employee and Team, because Employees can is members of teams. In addition, before introducing all of these CDM elements, I first give a very simple CDM diagram, is a model of our most familiar school scene, all the concepts mentioned below are reflected in the diagram, we can look at the following time to see:Р”Р‡irst, the definition of contact in the PD handbook is given: 'A relationship is a link between entities. But in the connection, the CDM has a relatively large expansion, in addition to preserving the ER diagram of the original relationship concept, but also increased the association,inheritance two kinds of entity relationships, Let's take a look at the usage of these relationships and the difference between them (the toolbar buttons that are labeled red are used to add these relationships to the entity).

Where the entity type corresponds to entity in the CDM, the attribute corresponds to the attribute of each entity in the CDM, which is basically one by one corresponding to the concept. CDM is based on the traditional ER diagram model theory, the ER diagram has three major elements: entity type, attribute and relation. Powerdesigner must seem jarring to those who follow that school of thought.CDM is the first model that most developers create when using PD, and is the abstraction at the highest level of the entire database design. There are other schools of thought, with their own experts, where conceptual data modeling is, in effect, 'relational lite'. It's a whole different way of looking at the world. In this sense, conceptual data modeling isn't just 'relational lite' at least as far as this school of thought is concerned.

An attribute could be a component of more than one relation with no problem at all. Notice that there is no such restriction in the relational data model. So if an attribute, say 'color' could be an attribute of hair, or of a car, it's necessary to qualify them as 'hair color' and 'car color' In order to identify each attribute uniquely. Many experts assert that an attribute can only be an attribute of one entity. The experts don't always agree on the exact meaning of the terms used in conceptual data modeling, or even necessarily on what conceptual data modeling really is.Р”В«ut Powerdesigner's restriction in this case is not unique to this product.

Powerdesigner many to many