The original text is from: http://www.voidcn.com/article/p-avzfndrz-oy.html
Conceptual data model
Conceptual Data Model (CDM): expresses the overall logical structure of data, which is independent of any software and data storage structure, that is, it is only for system analysts and application designers , A common language for mutual understanding between maintenance personnel and users, and does not target specific database platforms (such as Oracle or SQL Server) and tools (PowerBuilder). The objects contained in the CDM are usually not implemented in the physical database.
CDM can complete the following tasks:
- Data graphics and visualization
- Convert to PDM (Physical Data Model)
- Generate OOM (Object-Oritented MOdel, object-oriented model) class diagram
< li>Legal verification of data table design
Usually CDM uses Entity-Relation Graph (ER graph) to represent (the concept of “entity” and “relation”). Currently, E-R shows the most popular expression of CDM.
1. Basic concepts and conventions
1.1 Entity and attributes
An entity is an “object” that can be distinguished from other objects in the real world. It may be tangible or intangible, concrete or abstract , Living or inanimate.
Each entity has a set of characteristics, called entity attributes, which are used to describe the state and characteristics of the entity. For example: a certain employee, name: Diaosi, gender: male, these indicators represent the attributes of the entity of Diaosi.
The relationship between entities and attributes is shown in Figure 5-1.
Figure 5-1
1.2 Contact
Entity can be related to each other through relationship. According to the quantitative correspondence between entities, contacts can usually be divided into: One to One (One to One), One to Many (One to Many), Many to Many, Recursive (Recursive) Relationship) and Identify Relationship (Identify Relationship), etc.
many-recursive Contact Contact
1.3 domain
Domain is a certain or a certain some The value range of the attribute can be shared and used by the attributes of multiple entities after the domain is defined. The definition of the domain is of great significance in model design, making it easier to standardize the attributes in different entities.
1.4 Business rules
Business rules reflect the special data integrity constraints of the objects described by the information system. A business rule can be an industry standard, a customer requirement or a software development specification manual. When the information contained in the entity changes,
The system will check whether this information violates specific business rules. Therefore, before creating business rules, you must first clarify the constraint relationships that exist between the data.
2. Build a conceptual model
2.1 Determine business issues
Business process issues have been clarified in BPM, and on this basis, the information that needs to be stored is extracted. Including business-related entities, relationships between entities, special business rules, etc. These issues will become the basis for the establishment of CDM.
2.2 Establish a conceptual model
(1) Select the File-New Model command, and the window shown in Figure 5-2 will pop up. Select Conceptual Data Model.
Figure 5-2
(2) Click the “OK” button to open as shown in Figure 5-3 CDM workspace shown. The working area includes the browser window on the left, the design window on the right, the output window on the lower side and the floating tool window (Palette). You can use the icons in the tool window to design E-R diagrams in the design window.
Figure 5-3
(3) Establish entities and connections between entities.
3. CDM generates LDM
LDM is a new model of PowerDesigner 15, used to complete the logical design of the information system. Although LDM is still independent of the DBMS, it can design objects such as foreign keys, indexes, and views.
The specific method for CDM to generate LDM is as follows:
(1) Open the CDM model, select the Tools-Generate Logical Data Model command, and open the LDM Generation Options as shown in Figure 5-4 (Generate LDM option settings) window.
Figure 5-4
( 2) Select the Detail tab to set other options.
(3) Select the Selection tab, you can select CDM, entity, as shown in Figure 5-5.
Figure 5-5
(4) Click the “OK” button to start Generate LDM. As shown in Figure 5-7.
Figure 5-7
Note: The main content of LDM is between CDM and Between PDM.
4.CDM generates PDM
CDM completes the outline design of the information system, but it must be based on this in the physical design stage of the database The detailed background design is carried out on the above, and the design work at this stage can be completed only by converting CDM to PDM. Before CDM generates PDM, a DBMS must be selected as the target database, and the data type of the entity attribute defined in the CDM will be converted to the data type of the target database pair.
When CDM generates PDM, the objects in it must be converted into objects in PDM, that is, objects in the physical database.
The specific process of CDM generating PDM is as follows:
(1) Open the CDM model and select the Tools-Generate Physical Data Model command to open the window shown in Figure 5-8. Select the method and parameters of generating PDM in the General option. Select the Generate new Physical Data Model radio button to generate a new PDM, DBMS represents the target database management system (and version), Name represents the name of the target PDM, and Code represents the code of the target PDM. Select the Update existing Physical Data Model radio button to merge with the existing PDM to generate a new PDM.
Figure 5-8
(2) Select the Detail tab for detailed selection set up.
(3) Select the Selection tab and select the entity to be converted into a PDM table, as shown in Figure 5-9.
Figure 5-9
(4) Click the “OK” button to start generating PDM. If the Check model check box is selected in the Detail tab, warnings, errors, and prompts that occurred during processing will be displayed in the Result List window.
(5) Modify the warnings and errors according to the prompts.
(6) Generate PDM as shown in Figure 5-10. If the information displayed in the PDM is too much to be read, you can reduce the information by changing the Tools-Display Preferences command settings.
Figure 5-10
5. CDM generates OOM
When OOM is generated from CDM, PowerDesigner converts objects and data types in CDM into OOM objects and data types supported by UML language.
The specific steps for CDM to generate OOM are as follows:
(1) Open the CDM model and select the Tools-Generate Object-Oriented Model command to open the window shown in Figure 5-11.
Figure 5-11
(2) Select the Detail tab for other options setting.
(3) Select the Selection tab, you can select CDM, package and entity.
(4) Click the “OK” button to start generating OOM. The effect is shown in 5-12.
Figure 5-12
6. Summary
The above are generated by CDM The LDM, PDM and OOM models only transform the outline design of the system into relevant content, and generate a framework for the detailed audit of the system. After that, it needs to be further designed in LDM, PDM and OOM, for example: adding stored procedures in PDM, Triggers, design use case diagrams in OOM, etc.