Presentation Transcript

1. Lecture 3

   7/10/13
2. Upper SDLC SDLC (System development life-cycle) Set of activities, methods, best practices and deliverables that are used to develop and maintain information systems MS Visio known as Upper Case tool System Survey and Planning Analysis Design
3. Another Use Case Exercise BLine Design is a mail order clothing company. When a customer orders a particular item of clothing, customer service must get information on the product. Order status must be checked by customer service, and the product must be added to the order form. Meanwhile, shipping must update the order status, as well as the inventory. The must also view outstanding orders
4. An Introduction to designing a Database A database is a collection of data that is organized in such a manner that its contents can be readily accessed, managed and updated An Entity Relationship model (ERM) may be used to aid the development of a database An ER model may be represented pictorially by ERDs
5. What is a Data Model? A detailed model that captures overall structure of organizational data while being independent of any implementation considerations
6. Why use Data Modelling? Typically data modelling is carried out parallel with other requirements analysis and structuring steps during the systems analysis phase During this phase a data model is developed for the current system Following this, the data model supporting the scope and requirements of the proposed system is developed
7. ERD’s Entity Relationship Diagram is a form of data modelling Data modelling involves examining the data objects in a system and identifying the relationship between these objects
8. What is an Entity Relationship Diagram (ERD)? An ERD depicts data in terms of the entities and relationships described in an information system The primary purpose of an ERD is to document the logical structure of a database A logical representation of the data of an organization or business area in graphical form
9. Entity Relationship Diagramming Entity relationship modelling is a data modelingtechique, depicts a model that captures overall structure of organizational data while being independent of any implementation considerations. Entity – a thing of interest to the system Attribute – a piece of data about an entity Relationship – an association between two entities
10. An Entity An entity is a thing of interest to a system about which information is kept For example in a Hospital Administration System, some likely entities would include: Patient, Doctor, Operation, Ward Each of these things are of interest to the system and would have data stored about them
11. Entity Instance An entity instance is a single occurrence of an entity type. An entity type is described just once in a data model while many instances of that data type may be represented by data stored in the system. There is one EMPLOYEE entity type in most organisations but there may be hundred or thousands of instances of this entity type in the company.
12. An Attribute An attribute is an item of data held about an entity In computer systems an attribute is a field of information Example : Sales System Entity : Customer Attributes : Customer Name, Customer Address, Customer Phone Number
13. Attributes Continued.. A key attribute uniquely identifies a specific occurrence of an entity This may also be referred to as a primary key Examples of primary keys include: ISBN Student Number Staff ID
14. ERD Example
15. Babysitting System Employee Attributes: EmpID, Name, Address, Phone Number, Available Hours, JobNo Job Attributes: JobNo, JobDate, JobTime, EmpID Customer Attributes: CusNo, Name, Address, Phone Number, JobNo
16. ERD Example Example – Sales System A sale always starts with a customer receiving an estimate.The estimate then becomes an order. An order can be for one or more stock items. Each stock item belongs to a certain stock category (e.g. taps, sinks, cupboards etc.)
17. Choosing Entities Example A sale always starts with a customer receiving an estimate.The estimate then becomes an order. An order can be for one or more stock items. Each stock item belongs to a certain stock category (e.g. taps, sinks, cupboards etc.)
18. For Example In a Sales System, customer name and address are attributes of the entity customer The primary key is likely to be Customer Code or Customer ID as the the unique identifier for each customer in the system
19. ERD Relationships A relationship is an association between two entities that is important to the system. We must also consider the extent to which each entity is related to another.
20. Entity Relationships Remember: A relationship is an association between two entities that is important to the system. Example – Sales System A sale always starts with a customer receiving an estimate.The estimate then becomes an order. An order can be for one or more stock items. Each stock item belongs to a certain stock category (e.g. taps, sinks, cupboards etc.)
21. Primary key Acts as unique identifier for a single entity instance. E.g. StudentNo CustomerNo Staff No PPS No The values placed in primary key columns must be unique for each row: no duplicates can be tolerated. In addition, nulls are not allowed in primary key columns.
22. Our Example You are an accountant in a cell phone reseller company. You are interested in capturing data about customers, products and sales.