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    Dmbbb Dmbbb Presentation Transcript

    • DATA MODELBASIC BUILDING BLOCKS
    • The basic building blocks of all data models are: entities  attribute  relationship  constraint
    • END!!! PRESENTED BY:MARY JESETTE E. PEÑAOJAS BLIS-III PRESENTED TO: MS. GERALDINE G. MALLO (INSTRUCTOR)
    • An entity is anything (a person, a thing, or anevent) about which data are to be collectedand stores.An entity represents a particular type ofobject in the real world.Because an entity represents a particulartype of object, entities are distinguishable–that is, each entity occurrence is unique anddistinct
    • In data modeling an entity is some unit ofdata that can be classified and have statedrelationships to other entities.
    • Two related entities
    • Entities may be physical objects, such ascustomers or products but entities may alsobe abstraction such as flight routes or musicalconcerts.
    • An attribute is a characteristics of anentity. Attributes are the equivalent of fields infile system.
    • For example , a Customer entity be describedby attributes such as customer last name,customer first name, customer phone,customer address, and customer credit limit.
    • An entity with an attribute
    • A relationship describes an association amongentities.For example, a relationship exists betweencustomers and agents that can be described asfollows: an agent can serve many customers,and each customer may be served by oneagent.
    • Data models use three types ofrelationships: one-to-many, many-to-many,and one-to-one.Database designers usually use theshorthand notations 1:M or 1..*, M:N or *..*,and 1:1 or 1..1,respectively.
    • One-to-many (1:M or 1..*) relationship. A painter paints many different paintings, but each one of them is painted by only one painter. Thus, the painter (the “one”) is related to the paintings (the “many”). Therefore, database designers label the relationship “PAINTER paints PAINTING” as 1:M.
    • Many-to-many (M:N or *..*) relationship. An employee may learn many job skills, and each job skill may be learned by many employees. Database designers label the relationship “EMPLOYEE learns SKILL” as M:N.
    • One-to-one (1:1 or 1..1) relationship.  A retail company’s management structure may require that each of its stores be managed by a single employee. In turn,each store manager, who is an employee, manages only a single store. Therefore,the relationship “EMPLOYEE manages STORE” is labeled 1:1
    • A constraint is a restriction placed on thedata.Constraints are important because theyhelp to ensure data integrity.
    • Constraints are normally expressed in the formof rules. For example:An employee’s salary must have values thatare between 6,000 and 350,000. A student’s GPA must be between 0.00 and4.00.Each class must have one and only oneteacher