Ringkasan Materi #2 - Modeling Data in The Organization

Chapter 2: Modeling Data in The Organization

A Good Data Name: Related to business, not technical, characteristics, Meaningful and self-documenting, Unique, Readable, Composed of words from an approved list, Repeatable Written in standard syntax.

Data Definitions: Explanation of a term or fact Term–word or phrase with specific meaning, Fact–association between two or more terms.

Good data definition: A concise description of essential data meaning, Gathered in conjunction with systems requirements, Accompanied by diagrams, Achieved by consensus, and iteratively refined

E-R Model Constructs

• Entities: Entity instance–person, place, object, event, concept (often corresponds to a row in a table) Entity Type–collection of entities (often corresponds to a table)
  

• Relationships: Relationship instance–link between entities (corresponds to primary key-foreign key equivalencies in related tables), Relationship type–category of relationship…link between entity types

• Attributes: Properties or characteristics of an entity or relationship type (often corresponds to a field in a table)

Entities

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

Entity type – a collection of entities that share common properties or characteristics

Entity instance – A single occurrence of an entity type

An Entity…SHOULD BE: An object that will have many instances in the database, An object that will be composed of multiple attributes, An object that we are trying to mode

SHOULD NOT BE: A user of the database system, An output of the database system (e.g., a report)

• Strong entity exists independently of other types of entities, has its own unique identifier, identifier underlined with single line 
• Weak entity dependent on a strong entity (identifying owner)…cannot exist on its own, does not have a unique identifier (only a partial identifier), entity box and partial identifier have double lines, Identifying relationship links strong entities to weak entities

A Good Business Rule Is: Declarative–what, not how, Precise, agreed-upon meaning, one statement, Consistent–internally and externally, Expressible–structured, natural language. Distinct–non-redundant, Business-oriented–understood by business people.

Attribute–property or characteristic of an entity or relationship type

Classifications of attributes:

• Composite attribute – An attribute that has meaningful component parts (attributes)
• Identifiers (Keys)  – An attribute (or combination of attributes) that uniquely identifies individual instances of an entity type Candidate Identifier–an attribute that could be a key…satisfies the requirements for being an identifier, Will not change in value, Will not be null, Avoid intelligent identifiers (e.g., containing locations or people that might change) Naming Attributes, Name should be a singular noun or noun phrase, unique

Name should follow a standard format, e.g. [Entity type name { [ Qualifier ] } ] Class

Similar attributes of different entity types should use the same qualifiers and classes

The relationship type is modeled as lines between entity types…the instance is between specific entity instances

Relationships can have attributes : These describe features pertaining to the association between the entities in the relationship

Associative Entity–combination of relationship and entity, Ternary relationships should be converted to associative entities

Degree of Relationships : Unary, Binary, Ternary Relationship

Cardinality of Relationships

• One-to-One : Each entity in the relationship will have exactly one related entity

• One-to-Many : An entity on one side of the relationship can have many related entities, but an entity on the other side will have a maximum of one related entity

• Many-to-Many : Entities on both sides of the relationship can have many related entities on the other side
  

Sumber: PPT Dosen Pengampu Mata Kuliah Teknik Basis Data 2019/2020