The database system life database application system will stop using the entire period of starting planning, design, implementation, and maintenance to the last replaced by new systems. Database design input output
Three steps in the planning phase) System survey: a comprehensive survey of corporate organizations, draw organizational level, to understand the organization structure of the company 2) Feasibility analysis: establishment from technology, economic, efficiency, legal The feasibility of the database is analyzed; writing a feasibility analysis report; organizing experts to discuss its feasibility 3) Determining the total objectives of the database system and formulate project development plan demand analysis work 1) Analyze user activity, generate business flowchart 2) Determining system range, generating system range Figure 3) Analysis of data involved in user activity, generating data flow diagram 4) Analysis system data, generating data dictionary concept design, main step 1), data abstraction, design local concept mode 2) will be partial concept Mode Integrated into Global Concept Mode 3) Review Logic Design Physical Design ER Model: ER Figure Rule converts each entity type into a relational mode, entity's properties are the properties of the relational mode, the entity identifier is Conversion of the key dual contact type of the relational mode 1) If the entity connection is 1: 1, the key to any relationship mode can be added to the attribute of any relationship mode in two relational modes converted into two entity types. And the properties of the contact type. 2) If the physical relationship is 1: N, the attributes of the 1-----end entity type and the contact type of the contact type are added in the relational mode of the N-terminal entity type. 3) If the entity is related to M: N, the contact type is also converted into a relational mode. Its attribute is a key to the contact type of the contact type, and the key is a combination of the two-end entity key contact type. Conversion: The conversion of the two-dollar contact ternary contact type always converts the ternary contact type into a relational mode, its attribute is the key of the three-terminal entity type, and the key is the combination of the three-end entity key. Conversion example:
The design process of the ER model is basically two steps: · First design the entity type (not involved in "contact"); • Refer the design of the contact type (consider the connection between the entity). When designing, sometimes the boundary between the "entity" and "contact" is blurred. The database designer's task is to abstract the data between the real world and between the data, and use "entity" to "contact". In addition, the designer should note that the ER model should fully reflect the user's needs, and the ER model should be approved by the user to determine. Concept independent entity
Class and super-weak entity
Associated Type: ------------ ● ------------------------ ● ◇ -------- -------------- ●● ----------- ●
Associated couredient: Default: 0 .. * P: 1 .. * z: 0,1n: n
Erwin: Physical model can be forward, reverse engineering.
