Mobile Communication

Topic 3:The comparative database Model Performance Criteria appraise the basic relative sits basic components: entities, charges and relationships among entities. find and contrast various identifys. Explore integrity rules and explain the aboriginal types of integrities Design entities and their attributes. Continue Examine the importance of data dictionary. wrangle ERD components and how it affects database design and implementation.

Investigate data redundancy issues in the demoralise invoicing system Draw ERD diagram using C course of instructions Foot model A Logical V iew of Data Relational model View data logic all(prenominal)y rather than physically display panel Structural and data liberty Resembles a file conceptually Relational database model is easier to recognise than hierarchical and network models Tables and Their Characteristics Logical view of relational database is establish on relation Relation thought of as a table Table: two-dimensional structure composed of forms and columns inflexible commission of logical relation Contains group of related entities (entity set) separates each(prenominal) row in a table must be unequivocally identifiable mention: one or more attributes that look other attributes lists role is based on determination If you know the cherish of attribute A, you can follow the think of of attribute B operative dependence impute B is functionally dependent on A if all rows in table that agree in value for A also agree in value for B Types of Keys manifold describ e Composed of more than one attribute Key ! attribute Any attribute that is part of a key Superkey Any key that uniquely identifies severally row view key A superkey without unnecessary attributes Types of Keys (contd.) Entity integrity Each row (entity instance) in the table has its own unique identity Nulls No data entry Not permitted in primary key Should be avoided in other attributes Types of Keys (contd.) Can represent: An unheard-of attribute...If you want to reward a full essay, order it on our website: BestEssayCheap.com

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