Chapter 8 Review

Composite attribute

An attribute that has meaningful component parts.

Candidate key

An attribute, or combination of attributes, that uniquely identifies a row in a relation.

What elements of a DFD should be analyzed as part of data modeling?

Data stores, data flows, and processes all provide information for data modeling

Business rules

Specifications that preserve the integrity of the logical data model.

Degree

The number of entity types that participate in a relationship.

Which of the following types of relationships - one-to-one, one-to-many, many-to-many - can have attributes associated with them?

many-to-many

List the ideal characteristics of an entity identifier attribute.

Choose a candidate key that will not change its value Choose a candidate key that will never be null Avoid using intelligent keys Consider substituting single value surrogate keys or large composite keys

What is the degree of a relationship? Give an example of each of the relationship degrees illustrated in this chapter.

The number of entity types that participate in that relationship Agent to Car (1:1) Agent to Client (1:N) Property to Client (N:M)

Cardinality

The number of instances of entity B that can (or must) be associated with each instance of entity A.

What are the linkages among DFDs, decision tables, and E-R diagrams?

The relation between tables is identified using data flow between applications and is represented in ER diagram. In the similar way, decision table helps in both ER diagram and DFDs.

Domain

The set of all data types and values that an attribute can assume.

Discuss why some systems developers believe that a data model is one of the most important parts of the statement of information system requirements.

the characteristics of data captured during data modeling are crucial in the design of databases, programs, computer screens, and printed reports. data, not processes, are the most complex aspects of many modern information systems and hence require a central role in structuring system requirements. the characteristics about data (e.g., length, format, and relationships with other data) are reasonably permanent and have significant similarity for different organizations in the same business.

Overlap rule

Specifies that an entity instance can simultaneously be a member of two (or more) subtypes.

Partial specialization rule

Specifies that an entity instance of the supertype does not have to belong to any subtype.

Total specialization rule

Specifies that each entity instance of the supertype must be a member of some subtype in the relationship.

Disjoint rule

Specifies that if an entity instance of the supertype is a member of one subtype, it cannot simultaneously be a member of any other subtype.

Unary relationship

A relationship between instances of one entity type; also called recursive relationship.

Binary relationship

A relationship between the instances of two entity types. This is the most common type of relationship encountered in data modeling.

Repeating group

A set of two or more multivalued attributes that are logically related.

Ternary relationship

A simultaneous relationship among the instances of three entity types.

Entity instance

A single occurrence of an entity type. Also known as an instance.

Subtype

A subgrouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroupings.

Optional attribute

An attribute that may not have a value for every entity (or relationship) instance with which it is associated.

Multivalued attribute

An attribute that may take on more than one value for a given entity (or relationship) instance.

Required attribute

An attribute that must have a value for every entity (or relationship) instance with which it is associated.

Derived attribute

An attribute whose values can be calculated from related attribute values.

Associative entity

An entity type that associates the instances of one or more entity types and contains attributes that are peculiar to the relationship between those entity instances.

Identifier

A candidate key that has been selected as the unique, identifying characteristic for an entity type.

Entity type

A collection of entities that share common properties or characteristics.

Conceptual data model

A detailed model that captures the overall structure of organizational data that is independent of any database management system or other implementation considerations.

Entity-relationship data model (ERD)

A detailed, logical representation of the entities, associations, and data elements for an organization or business area.

Supertype

A generic entity type that has a relationship with one or more subtypes.

Entity-relationship diagram

A graphical representation of an E-R model.

List the deliverables of the Conceptual Data Modeling part of the analysis phase of the systems development process.

Entity-relationship (E-R) diagram UML class diagram a set of entries about data objects to be stored in repository project dictionary, or data modeling software

Contrast the following terms: a. Subtype; supertype b. Total specialization rule; partial specialization rule c. Disjoint rule; overlap rule d. Attribute; operation

a. *Subtype* is a sub grouping of the entities in an entity type; *Supertype* is a generic entity type that has a relationship with one or more subtypes b. *Total specialization* specifies that each entity instance of the supertype must be a member of some subtype in the relationship; *Partial specialization* specifies that an entity instance of the supertype does not have to belong to any subtype, and may or may not be an instance of one of the subtypes c. *Disjoint rule* specifies that if an entity instance of the supertype is a member of one subtype, it cannot simultaneously be a member of any other subtype; *Overlap rule* specifies that an entity instance can simultaneously be a member of two (or more) subtypes d. *Attribute* is a named property or characteristic of an entity that is of interest to the organization; *Operation* is business rules that protect the validity of attribute values and the scope may be limited to attributes within one entity

Triggering operation (triggers)

an assertion or rule the governs the validity of data manipulation operations such as insert, update, and delete, also called a trigger.

What is the significance of triggering operations and business rules in the analysis and design of an information system?

triggering initiates causes and effects that keeps the business moving while business rules lays the foundation on to which the business is built upon

When must a many-to-many relationship be modeled as an associative entity?

when there are attributes associated with the relationship

Distinguish between the data modeling done during information systems planning, project initiation and planning, and the analysis phases of the SDLC

*Planning:* Enterprise-wide data model Conceptual data model *Analysis:* Conceptual data models *Design:* Logical data model

Attribute

A named property or characteristic of an entity that is of interest to the organization.

Relationship

an association between the instances of one or more entity types that is of interest to the organization.