Mobile Communication

Topic 3:The comparative database Model Performance Criteria define the basic relative sits basic components: entities, charges and relationships among entities. take and contrast various secerns. Explore integrity rules and explain the cardinal 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 blue invoicing system Draw ERD diagram using C lyrics Foot model A Logical View of Data Relational model View data logic anyy sort of than physically display panel Structural and data license Resembles a file conceptually Relational database model is easier to empathise than hierarchical and network models Tables and Their Characteristics Logical view of relational database is ground on relation Relation thought of as a table Table: two-dimensional structure composed of grades and columns unrelenting 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 regularise other attributes tonalitys role is based on determination If you know the cherish of attribute A, you can delimit the think of of attribute B operative dependence put 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 abstruse notice Composed of more than one attribute Key attribute An y attribute that is part of a key Superkey ! Any key that uniquely identifies severally row expectation 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 unknown region attribute...If you want to reward a full essay, order it on our website: BestEssayCheap.com

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