Conceptual Design Lecture 3 Database Development

Aim of this presentation  To introduce noun identification  To introduce the diagram script  To identify how we use the Information base to help inform the ER Diagram

Entity Relationship Diagrams The output for the Conceptual design is two things. –An ER Diagram –A diagram script

ER Diagram STUDENT HALL N:1 StudentID HallName Entity Entity Name Relationship Cardinality Attribute Attribute name Mandatory Existence Optional Existence

Diagram Script Entity name Attributes IdentifiedSynonymRelated to The name of the entity identified. (Singular) Any attributes identified for the entity. No spaces allowed in the Attribute name. Alternative name for entity identified from the information base Entities which it relates to.

Diagram Script Entity nameAttributes IdentifiedSynonymRelated to Coursetitle courseCode PrerequisiteStudent Class Course StudentstudentID studentName address postcode Course Classsemester classRoom uniqueClassName tutor Course Relationship between course and student gradeCourse and Student

Using the Information Base  Where do we start?  Analyse the information gathered during the requirements analysis. –One element at a time

Using the Information Base Identifying Entities using noun identification.  In noun identification we follow this procedure: –Examine the system descriptions and identify the nouns and noun phrases –Reject any which seem unsuitable candidates for being entities.

Identifying Entities  A noun is a word that names a person or thing  A noun phrase is a group of words that operate like a noun e.g. dentist appointment  Consider each noun or noun phrase and determine if it is a candidate entity.  Reasons for rejecting candidate entities.

Rejecting Candidate Entities  Redundancy  Vagueness  An event or operation  Meta Language  Outside the system boundary  Attribute

What we know about an Entity  Entity contains descriptive information.  An entity is anything about which we store information.  An entity is a "thing", "concept" or, object".  If a data object you have identified is described by other objects, then it is an entity.

What we know about an Attribute  An attributes either identifies or describes an entity.  Attributes that identify entities are called key attributes, these attributes would uniquely identify an entity instance.  Attributes that describe an entity are called non-key attributes.

Sample Description The local Sea Cadet Unit records information on the Cadets belonging to the unit. For each cadet they record name, address and one emergency contact telephone number. The cadets take classes each week for different skills. Records of skills achieved are recorded, along with the date achieved.

Identify the nouns and noun phrases The local Sea Cadet Unit records information on the Cadets belonging to the unit. For each cadet they record name, address and one emergency contact telephone number. The cadets take classes each week for different skills. Records of skills achieved are recorded, along with the date achieved.

Diagram and Script Cadet Entity nameAttributes IdentifiedSynonymRelated to CadetFName, Surname, Add1, Add2, Add3 PostCode, ConTelNo Class Skill ClassWeekCadet SkillCadet Relationship between Cadet and Skill Date AchievedSkill Cadet Class M:N Skill M:N

Diagram and Script  Once you have dealt with the System Description you then look at each type of information base and check that that information base element is catered for.

Cadet Record Card Date Rank Cadet ID Name Address Contact Telephone

Revised diagram Cadet Entity nameAttributes IdentifiedSynonymRelated to CadetCadetID, Rank, FName, Surname, Add1, Add2, Add3 PostCode, ConTelNo Class Skill ClassWeekCadet SkillCadet Relationship between Cadet and Skill Date AchievedSkill Cadet Class M:N Skill M:N CadetID

 Work through each piece of information base to produce your diagram.  Finally check what additional requirements the company will have for the new system and ensure that your initial design can cater for those requirements.

Summary We have seen  How to use noun identification for identifying entities and attributes.  How to produce the diagram script  How to use the information base to inform the ER Diagram and script

Next Week  In-class test revision  Practice in-class test questions