PowerDesigner concept data model (CDM) Description

ConceptualDataModel: conceptual data model, which is based on the Entity-RelationShip (E-R) theory and is expanded. It starts from the user

Conceptual Data Model: Conceptual Data Model, which is based on the Entity-RelationShip (E-R) theory and is expanded. It starts from the user

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PowerDesigner 15 Overview

This article mainly describes the CDM model and its usage.

1. Overview of concept data model (CDM)Conceptual Data Model: Conceptual Data Model, which is based on the Entity-RelationShip (E-R) theory and is expanded. It models information from the user's point of view and is mainly used for Conceptual Design of databases.

Generally, people first abstract the real world into a conceptual world, and then convert the conceptual world into a machine world. In other words, objective objects in the real world are first abstracted as entities and Relationship. They do not depend on a specific computer system or a DBMS system, this model is what we call CDM, and then converts CDM to the data model supported by a DBMS on the computer. This model is the physical data model, that is, PDM.

CDM is a set of strictly defined model elements that accurately describe the static characteristics, dynamic characteristics, and integrity constraints of the system, it consists of three parts: data structure, data operation, and integrity constraint.

1) Data structures are expressed as entities and attributes;

2) The data operation table is the insert, delete, modify, query, and other operations of records in the entity;

3) integrity constraints are expressed as integrity constraints of data (such as data types, checks, rules, and so on) and referential integrity constraints between data (such as links and inherited links)

Ii. Definitions of entities, attributes, and identifiers

2.1 Entity ):

It is also called an instance, which corresponds to "events" or "things" that can be different from other objects in the real world ". For example, each student in the school and each operation in the hospital. Each entity can be used to describe a set of properties of entity features, which are called attributes. An entity is described by several attributes. For example, a student entity may consist of attributes such as student ID, name, gender, date of birth, department, and year of admission.

2.2 entity set ):

Is a set of entities of the same type and nature. For example, a set of all students in a school can be defined as a "student" entity set, each entity in the "student" entity is subject to a student ID, name, gender, date of birth, department, and year of admission.

2.3 entity type ):

Is a collection of the common nature of each entity in an entity set. For example, the "patient" entity type is: Patient {outpatient number, name, gender, age, ID card No .............}. An object is an instance of the object type. When the meaning is clear, the object and object types are usually used interchangeably. Each entity in an object type contains one or more attributes that uniquely identify it. These attributes are called identifiers of an object type. For example, a student ID is an Identifier of a student entity type, "name", "Date of Birth", and "email address" form the "Citizen" entity type identifier. Some object types can have several groups of attributes that act as identifiers. select one of these attributes as the primary identifier of the object type, and others as the secondary identifier.

3. entity, attribute, and identifier expression

4. Create a conceptual data model4.1 SELECT File --> New. In the displayed dialog box, select CDM model (Conceptual Data Model) to create a model.

4.2 create a conceptual data model. To give a brief introduction to the current workspace.

4.3 select the newly added CDM model, right-click it, and select "Properties" from the pop-up menu. the pop-up dialog box is displayed.In the General tab, you can enter the name, code, description, creator, version, and default chart of the created model. Enter the description and description in the "Notes" tab. For More tags, click "More>.