DBAD Flashcards
A Data Dictionary stores:
Attribute name Entity Data Type Size Validation Key
A Data Dictionary is:
A catalogue of all data items in a system
Types of validation are:
Presence check
Range check
Restricted choice check
Lookup
Purpose of a data dictionary
Provides a detailed description of all data items that are in the system to ensure the validity and reliability of the data contained
What is an entity event matrix?
A model to consider the entities in a system over a period of time
Purpose of an Entity Event Matrix
Is used to record a list of all events that can occur and shows the effect they have on the entities within the system
Purpose of an Entity Life History Diagram
Is used to record the sequence of events that can occur within any one entity.
It also indicates alternate and repeated events
What is a Data Flow Diagram (DFD)?
Provides a graphical, non-technical representation of the system under consideration
What is a Physical DFD?
Represents the system currently in use. It shows the actual way in which the system operates (Is implementation-dependant)
What is a logical DFD?
It focuses on data flows between process without specifying physical characteristics (Implementation-independent)
Purpose of a DFD
Provides a graphical representation of the components in the system. Shows input/output of data & movement of data between processes
What does a DFD show?
Input/Output of data from/to entities that exist outside the system
Movement if data between processes & data stores that are inside the system
Level 0 DFD (Context Diagram)
Shows a simple representation of the entire system.
It shows an overall Summary of the data flowing into and out of the system
Level 1 DFD
Provides an overview of all major processes within the system
Components of a DFD
Data flows Physical flows External entities Data stores Processes
Conceptual design
A model of the information used within the business/organisation is constructed. Shows entities & relationships that will exist in new system. Independent of all physical considerations
Logical design
See pp
Physical design
Is produced after logical design. Provides a description of the database implementation in terms of storage devices, file organisation & security features
Reasons why conceptual & logical design are separated from physical design
See pp
System refinement
See pp
Methods used to produce a Process Specification:
Standard English, Structured English, Graphical design notations
Standard English
A few paragraphs of every day English would be used to describe a bottom level process
Disadvantages of using Standard English
See pp
Advantage of using Standard English
Natural language of both analyst, client & users therefore no additional learning.
Structured English
Uses a restricted subset of the English language that can be easily coded and resembles a programming language. Clearly shows hierarchy of actions & events E.g. IF…ELSE…IF END, LOOP…LOOP END
Graphical design notation: Structure charts…
Provide a means of breaking down a complex process and illustrating the components of the process diagrammatically
A structure chart will show…
The sequence of events & activities, Any repetition (or iteration) of events, Any optional events
What is a structure chart?
A hierarchical diagram that shows the relationships between the functions and actions that take place within a process
Other graphical design notations/techniques
System flow charts, decision tables, decision trees, organisation charts
Physical database design involves:
The selection of appropriate database management software, Deciding how to represent the logical model using the DBMS selected
Importance of user interface design
More intuitive the user interface is, the easier it is to use. Better it is, easier to train people to use it, reducing training costs. Better it is, more users will like & want to use it, increasing client’s satisfaction
Purpose of user interface:
Provide a front-end to the database system that allows users to interact with it without having to think about the underlying structures. Users want to find the information they need quickly with minimal amount of effort.
User interface design includes:
Determining the type & interaction styles for user interface, Determining the layout of any screen forms, Planning the use that will be made of menus to allow users to interact with the system
The design work (of user interface) should define:
How data entry screen should look, how menus will be organised into commands & sub menus, shortcut keys available, type of control used for data entry (text/list/check box), colour & navigation scheme etc.
