Entities and Attributes

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  • Conceptual model: A data model, usually represented by an entity relationship diagram (ERD)
    • The client dream would be the conceptual model
  • Physical model: A design for an object (a car, a house, a database, etc) which includes implementation details such as size, volume, weight, etc)
    • The physical reality will become the physical model
  • All many-to-many relationships must be reduced to a set of on-t--many relationships

Database Normalization

Many people unfamiliar with database design principles often ask, “Why not just put all the data in one big table?” This single-table approach leads to problems of data redundancy (duplication) and data anomalies (data inconsistencies).

To avoid these data issues, database normalization is used to create a design that reduces or eliminates data redundancy and, therefore, avoids data anomalies. In general, normalization helps database designers determine which attributes, or fields, belong to each entity. In turn, this information helps determine which fields belong in each table. Normalization is a multistage process that enables designers to take the raw data to be collected about an entity and develop the data into a structured, normalized form that reduces the risks associated with data redundancy. Data redundancy poses a special problem in databases because storing the same data in different places can cause problems when updates or changes to data are required.

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