logical database design 逻辑设计

From ER Model to Relational Model • Our method of designing relational (logical) model uses information from ER Model — We assume that ER modelling is performed before relational modelling • Informally, ER Model — Partitions information in a domain into Entities (boxes) and attributes — Links entities up into a network to reflect the relationships from the real world domain — The network of entities represents the real world domain • Informally, relational model — Partitions information into tables (relations) — Links tables up into a network to reflect the relationships existing among data — The network of tables store data from the real world domain • We can notice similarities between ER Models and Relational Models — Entities correspond to Tables (relations) — Network of entities correspond to network of tables 实体对应表即关系 实体网络对应表网络

Step-by-Step Procedure for Logical Database Design • Derive relations for logical data model • Validate relations using normalization • Validate relations against user transactions • Check integrity constraints • Review logical data model with user • Merge logical data models into global model (optional) • Check for future growth  重要的是前两个步骤 逻辑数据模型推导关系和使用规范验证关系

Entities & their Attributes • Individual tables are derived from strong entities (entities with a clear Primary key) • Fields in the tables are derived from attributes associated with entities — Define the data types of the fields • Define the primary key of the table  • Foreign keys are decided later while modelling the relationships — Not all tables (relations) have foreign keys — At this stage, however, bear in mind that relation model is incomplete without deciding foreign keys 表个体都来自