MIS 333 Chapter 2

4 Criteria for selecting identifiers for entities

1. Choose an identifier that will not change its value over the life of each instance of the entity type 2. Choose an identifier such that for each instance of the entity, the attribute is guaranteed to have valid values and not be null (or unknown). 3. Avoid the use of so-called intelligent identifiers (or keys), whose structure indicates classifications, locations, and so on 4. Consider substituting single-attribute surrogate identifiers for large composite identifiers.

4 types of cardinality constraints and draw example of each

1. Mandatory one 2. Optional one 3. Mandatory many 4. Optional Many

Entity

A person, a place, an object, an event, or a concept in the user environment about which the organization wishes to maintain data.

Attribute

A property or characteristic of an entity or relationship type that is of interest to the organization

Unary Relationship

A relationship between instances of a single entity type.

Binary Relationship

A relationship between the instances of two entity types

Cardinality Constraint

A rule that specifies the number of instances of one entity that can (or must) be associated with each instance of another entity.

Ternary Relationship

A simultaneous relationship among the instances of three entity types.

Entity Instance

A single occurrence of an entity type.

Business Rule

A statement that defines or constrains some aspect of the business. It is intended to assert business structure or to control or influence the behavior of the business.

Explain where you can find business rules in an Organization

Business rules appear (possibly implicitly) in descriptions of business functions, events, policies, units, stakeholders, and other objects. You can find these descriptions in interview notes from individual and group information systems requirements collection sessions, organizational documents (e.g., personnel manuals, policies, contracts, marketing brochures, and technical instructions), and other sources.

Composite Attribute Vs. Multi valued Attribute

Composite Attribute=An attribute that has meaningful component parts (attributes). Multi valued Attribute=An attribute that may take on more than one value for a given entity (or relationship) instance

Simple Attribute Vs. Composite Attribute

Composite Attribute=An attribute that has meaningful component parts (attributes). Simple Attribute=An attribute that cannot be broken down into smaller components that are meaningful to the organization.

Degree Vs. Cardinality

Degree=The number of entity types that participate in a relationship. Cardinality= represent how many entities of one kind relate to how many entities of another kind

Stored Attribute Vs. Derived Attribute

Derived Attribute=An attribute whose values can be calculated from related attribute values Stored Attribute= are such attributes which are already stored in the database and from which the value of another attribute is derived

Required Attribute Vs. Optional Attribute

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

Give an example of a weak entity type. Why is it necessary to indicate an identifying relationship?

Room in a Building It is necessary because it helps those interacting with the database to know which entity the weak entity actually correlates with so they can match them up

Ternary Relationship Vs. Three Binary Relationships

Ternary Relationship= A simultaneous relationship among the instances of three entity types. Three Binary Relationships= 3 separate relationships among the instances of two entity types. This is how a ternary relationship has to be draw with an associative entity

Degree

The number of entity types that participate in a relationship.

What is the degree of a relationship? List the 3 types of relationship degrees described in the chapter and give examples of each

The number of entity types that participate in a relationship. 1. Unary - is married to 2. Binary - student registers for a course 3. Ternary - vendor, part, and warehouse

Identifying Relationship

The relationship between a weak entity type and its owner

Strong Entity Type Vs. Weak Entity Type

Weak Entity Type=An entity type whose existence depends on some other entity type. Strong Entity Type=An entity that exists independently of other entity types.

3 conditions that suggest the designer should model a relationship as an associative entity type

1. All the relationships for the participating entity types are "many" relationships. 2. The resulting associative entity type has independent meaning to end users and, preferably, can be identified with a single-attribute identifier. 3. The associative entity has one or more attributes in addition to the identifier 4. The associative entity participates in one or more relationships independent of the entities related in the associated relationship.

4 Reasons why a business rule approach is advocated as new paradigm for specifying information systems requirements

1. Business rules are a core concept in an enterprise because they are an expression of business policy and guide individual and aggregate behavior. Well-structured business rules can be stated in natural language for end users and in a data model for systems developers. 2. Business rules can be expressed in terms that are familiar to end users. Thus, users can define and then maintain their own rules 3. Business rules are highly maintainable. They are stored in a central repository, and each rule is expressed only once, then shared throughout the organization. Each rule is discovered and documented only once, to be applied in all systems development projects 4. Enforcement of business rules can be automated through the use of software that can interpret the rules and enforce them using the integrity mechanisms of the database management system

3 Reasons why system designers believe that data modeling is the most important part of the SDLC

1. The characteristics of the data obtained during the data modeling is crucial in designing the databases, print reports, programs and computer screens. 2. When compared to processes, data is the most complex aspect for many modern information systems. Hence it plays a crucial role in documenting system requirements. 3. The information used in the data modeling can be used in identifying primary keys, foreign keys, relational tables, procedures and triggers. 4. The structured information about data is extremely important for generating the programs automatically.

6 General Guidelines for naming data objects in a data model

1.Relate to business, not technical (hardware or software), characteristics 2.Be meaningful 3.Be unique 4.Be readable 5.Be composed of words taken from an approved list 6.Be repeatable 7. Follow a standard syntax

Entity Type

A collection of entities that share common properties or characteristics.

Entity Relationship Model

A logical representation of the data for an organization or for a business area, using entities for categories of data and relationships for associations between entities.

Relationship Type

A meaningful association between (or among) entity types.

Identifier

An attribute (or combination of attributes) whose value distinguishes instances of an entity type

Composite Attribute

An attribute that has meaningful component parts (attributes).

multivalued attribute

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

Derived Attribute

An attribute whose values can be calculated from related attribute values

Strong Entity

An entity that exists independently of other entity types.

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

Weak Entity

An entity type whose existence depends on some other entity type.

What else should a relationship definition explain besides what action is being taken?

And why it is important, any optional participation, the reason for any explicit maximum cardinality, any mutually exclusive relationship, any restrictions on participation in the relationship, the extent of history that is kept in the relationship, whether an entity instance involved in a relationship instance can transfer participation to another relationship instance, and give examples

Entity Type Vs. Relationship Type

Entity Type=A collection of entities that share common properties or characteristics. Relationship Type= A meaningful association between (or among) entity types.