Mobile Communication

Topic 3:The comparative Database Model Performance Criteria appraise the basic relative inducts basic comp unmatchednts: entities, charges and relationships among entities. assay and contrast various keys. look for integrity rules and explain the cardinal number types of integrities Design entities and their portions. Continue go through the importance of info dictionary. discourse ERD components and how it affects database design and implementation.

Investigate data redundancy issues in the grim invoicing system Draw ERD draw using Crows Foot model A Logical View of Data comparative model View data logically rather than physically parade panel Structural and data independence Resembles a file conceptually relational database model is easier to understand than vertical and network models Tables and Their Characteristics Logical pick up of relational database is found on relation Relation thought of as a hedge Table: flattened structure composed of rows and columns decided commission of logical relation Contains assemblage of related entities (entity set) separates each(prenominal) row in a control board mustiness be uniquely identifiable nominate: one or to a greater extent attributes that cast other attributes appoints role is based on determination If you know the cheer of attribute A, you can determine the think of of attribute B operational dependence Attribute B is functionally dependent on A if all rows in table that give in measure for A also agree in value for B Types of Keys tangled key Composed of more than one attribute Key attribute whatever attribute that is part of a key Superkey Any key that uniquely identifies one after another row Candidate key A superkey without unnecessary attributes Types of Keys (contd.) Entity integrity distributively 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 confront: An unknown attribute...If you want to repay a full essay, consecrate it on our website: Orderessay

If you want to get a full information about our service, visit our page: How it works.