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Entity-Relationship Model

Course Objectives. Define each of the following key terms: entity type, attribute, relationship, cardinality, weak entity, gerund, generalization, supertype, subtype, inheritanceDraw an entity-relationship (E-R) diagram to represent common business situations.Distinguish between unary, binary, and ternary relationships, and give an example of each.Model ISA relationships in an E-R diagram..

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Entity-Relationship Model

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    1. Entity-Relationship Model Reporters: Harriet B. Fernandez Michelle Saab

    2. Course Objectives Define each of the following key terms: entity type, attribute, relationship, cardinality, weak entity, gerund, generalization, supertype, subtype, inheritance Draw an entity-relationship (E-R) diagram to represent common business situations. Distinguish between unary, binary, and ternary relationships, and give an example of each. Model ISA relationships in an E-R diagram.

    3. Database Development Process

    4. Analogous to analysis phase of software development Requirement Collection and Analysis - Designers interview database users to understand and document data requirements. Functional Requirements - User defined operations to be applied on the database Database Design and Conceptual Data Model

    5. Conceptual Design -Conceptual schema; a permanent description of database specifications. - Capture the semantics of the data; description of data, constraints, relationships - No storage details needed Database Design and Conceptual Data Model (contd.)

    6. E-R Model A detailed, logical representation of the entities, associations, and data elements for an organization or business area. E-R model is normally expressed as an entity – relationship diagram (E-R diagram), which is a graphical representation of an E-R model.

    7. Sample E-R Diagram

    9. ENTITIES A person, place, object, event, or concept in the user environment about which the organization wishes to maintain data. Examples: Person: EMPLOYEE, STUDENT, PATIENT Place: STATE, REGION, COUNTRY Object: MACHINE, BUILDING, AUTOMOBILE Event: SALE, REGISTRATION, RENEWAL Concept: ACCOUNT, COURSE, WORK CENTER Use capital letters in naming an entity type. SYMBOL:

    10. Entity Types and Entity Instances Entity Type (entity class) A collection of entities that share common properties or characteristics. Entity Instance (instance) A single occurrence of an entity type. EXAMPLE

    12. ATTRIBUTES Each entity type has a set of attributes associated with it. An attribute is a property or characteristic of an entity that is of interest to the organization. Examples: (entity types and associated attributes) STUDENT: STUDENT NO., NAME, ADDRESS, PHONE NO. AUTOMOBILE: VEHICLE ID, COLOR, WEIGHT, HORSEPOWER EMPLOYEE: EMPLOYEE NO., NAME, ADDRESS, SKILL We use capital letters in naming an attribute. In E-R diagrams, we represent an attribute by placing its name in an ellipse with a line connecting it to its associated entity.

    13. Candidate Keys and Primary Keys A candidate key is an attribute (or combination of attributes) that uniquely identifies each instance of an entity type. A primary key is a candidate key that has been selected as the identifier for an entity type. Example

    15. Multivalued Attributes A multivalued attribute can have more than one value for each entity instance. Example:

    16. RELATIONSHIPS A relationship is an association between the instances of one or more entity types that is of interest to the organization. A relationship is indicated by a diamond shape. Attributes (or properties) may be associated with a many-to many relationship, as well as an entity. Example

    18. Degree of a Relationship A unary relationship, also called a recursive relationship, is a relationship between the instances of one entity type Binary Relationship is a relationship between instances of two entity types and is the most common type of relationship encountered in data modeling

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