Monday, September 24, 2012

Part 3: How to Data Model



3.1: Identify Entity Types

Entity

Object that can be observed and classified by its properties and characteristics

Business definition with a clear boundary

Characterized by a noun


Example: Product, Employee

3.2: Identify Attributes

Attributes


Characteristics and properties of entities

Example :

Book Id, Description, book category are attributes of entity “Book”

Attribute name should be unique and self-explanatory

Primary Key, Foreign Key, Constraints are defined on Attributes

Relationship


3.3: Identify Relationships

Relationship between entities - structural interaction and association

described by a verb

Cardinality

1-1
1-M
M-M


Example : Books belong to Ambarish


3.4: Apply Naming Conventions

Naming Standards


1. Be correct, that is, both functionally and technically accurate.
2. Be clear, avoiding the use of vague terms such as “handle” or "process.”
3. Be concise, using the fewest number of words possible, avoiding articles and needless prepositions.
4. Be unique, avoiding wording similar to that of any other name.
5. Be atomic, representing only a single concept.
6. Contain only letters of the alphabet, numbers, and word separators.
7. Follow the specified format for names
8. Reflect common terminology used throughout Federal Student Aid.
9. Use complete names wherever possible instead of abbreviations or acronyms.
10. Use only approved abbreviations or acronyms when the data modeling tool restricts the length of the name.


3.5: Assign Keys


Keys

Super Key
Primary Key
Candidate Key
Secondary Key

Super Key

A super key is a column or set of columns that uniquely identifies a row within a table.

Given table: EMPLOYEES{employee_id, firstname, surname, sal}

Possible superkeys are:

{employee_id}
{employee_id, firstname}
(employee_id, firstname, surname, sal}

Only the the minimal superkey - {employee_id} - will be considered as a candidate key.