CBAD2103Data Analysis and Modeling

Chapter 7Conceptual Design Methodology

CONCEPTUAL DESIGNING PHASE

1. Determination of entity;2. Determination of relationship;3. Determination of attribute for entity and relationship;4. Determination of domain for attribute;5. Determination of primary key; and6. Re-evaluation of data model with users.

ENTITY DETERMINATION

The determination of an entity in a given particular environment is the firstthing you have to do.

The usual method used to determine entity is toexamine the requirement specification of users. implementing each class.

RELATIONSHIP DETERMINATION

Worker Works Company

Students Register Course

Manager Supervises Staff

DETERMINING ATTRIBUTE FOR ENTITY OR RELATIONSHIP

Attribute can be determined when the noun mentioned constitutes a property, quality, identifier or characteristic of any of these entities or relationships modeled in database.

In recognizing attributes, it is important for you to model the attributes as simple or composite, solitary, multi-valued or derived attribute.

All attributes must be documented.

DETERMINING ATTRIBUTE DOMAIN

The main purpose of this step is to determine the domain for each modeled attribute. A Domain is the type of value permitted for each attribute.

The following are examples of how you can determine attribute domain.

◦ Attribute Domain for Worker No is five characters with the first two characters represented by letters of the alphabet and the rest by digits ranging from 1 to 999.

◦ Attribute Domain for Gender is either F or M which is an alphabet character.

DETERMINING KEY

A key candidate is an attribute or a set of minimum attributes that uniquely recognizes occurrences in an entity.

When choosing a primary key from several possible key candidates you may want to use the following guidelines:

◦ The key candidate with the minimum attribute sets.◦ The key candidate that is least likely to have its values

changed.◦ The key candidate with the shortest characters (for key

candidate from the character domain).◦ The key candidate with lowest maximum value (for a key

candidate from the numeric domain).◦ The key candidate that is the easiest to use by users of the

system.

Tutorial 1

Chapter 8Normalization

PURPOSE OF NORMALIZATION

Technique of determining and evaluating the resultant logical data model to ensure that it is accurate as well as containing the minimum amount of anomalies.

The process of normalization is a formal method of determining relationships based on the primary key or candidate key and of functional dependency between attributes.

Relationships which contain the element of excess data often cause problems known as anomalies of updating.

The concept of updating anomalies:(i) insertion anomaly(ii) deletion anomaly(iii) modification anomaly

FUNCTIONAL DEPENDENCY

If A and B are attributes of the H relationship, B is said to be functionally dependent on A (represented as A-) if each value of A is only connected to only one value of B.

NORMALIZATION PROCESS

The purpose of normalization is to minimize anomalies found in each relationship.

Through this process, relationships which contain excess data and high anomalies will be divided into several tables which contain the minimum number of anomalies.

1NF Form

Unusual form (UNF) is a table relationship which contains one or more repetitive groups.

The first normalization form (1NF) is a relationship which crosses between each row and column containing only one value (fulfils relationship characteristics).

Each relationship or table in the UNF form must be normalized to 1NF form.

The change to 1NF form is done by identifying the repetitive group and remove it from the relationship mentioned

2NF Form

The second normalization form (2NF) is based on the concept of full functional dependency.

To clarify the concept of full functional dependency, consider the following relationship:

The second normalization form (2NF) is a relationship which is already in 1NF form and each attribute is not the full functional dependency key of the overall primary key.

3NF Form

The third normalization form (3NF) is a relationship which is already in the form of 1NF and 2NF and there are no non-key attributes which are transitively dependent on the primary key.

Project (ProjectNo, ProjectName, WorkerNo, Date of Birth)ProjectNo - ProjectName, WorkerNoWorkerNo - Date of BirthBased on the concept of transitive dependency, ProjectNo - Date of Birth