Elements of Database System Database Design Technique process

Elements of Database System Database Design Technique • process of database design consist of three major phases • an information requirement analysis phase • a logical design phase • physical design phase

Elements of Database Systems An information requirement analysis phase involves: 1 st & most Imp phase ◦ Working with users to define their information needs in detail ◦ Information as users see it ◦ Information is viewed in terms of the way it appears in documents. ◦ On terminal screens ◦ Even images in users mind

Elements of Database System Logical design ◦ Various views have been defined and specification developed, they must be coordinated and organized into an integrated cohesive system. ◦ Process referred to as logical design 1. Developing a data model for each user view 2. Integrating the entities, attributes, and relationship into a composite logical schema that describes the database for that module in terms unrelated to the sw package being used

Elements of database 3. Transforming the logical schema into a software schema expressed in the language of the chosen database management package.

Elements of database A Primary Key Uniquely identifies each data item in a group of related items. A primary key is a data item with only single headed arrow. Concatenated keys Are formed by joining two or more data items to produce a primary key A one to many relationship exists between one of the other elements of the group and the key

Un-normalized bubble chart High degree Instructor Course Prospect date Title year university Text book Organizatio n fee stree t City zip

Un-normalized bubble chart The last figure is said to be unnormalized; becz it has many-to-many relationships between data items in the same group and one-to-many relationship between non-key items in the same group. We need to normalize it; means keys have only single headed arrows to items within their data group, although they can have one-to-many relationships with keys of other data

Normalized bubble chart High degree Instructor Course + Date Prospect university Standard fee Text book Title zip Organizatio n stree t City year

Rules to normalize the bubble chart If a bubble has single headed arrows entering it from other items in its group and leaving it to other items in its group, it is a potential primary key and should be moved into a new group with the items it identifies. If an items or a group of items has no key, a concatenated key should be formed to serve as an identifier. Names (of people, courses, products), identification numbers (social security number, account number), and dates are likely candidates for concatenated keys)

Rules to normalize The concatenated key should be formed from the fewest number of data items possible to identify the data items in its group

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