SYSTEM MODELLING

Question 1

What is system modeling

Answer 1

This is the process of developing abstract models of a
system, with each model presenting a different view or
perspective of that system

Question 2

What is the importance of system modeling to the analyst?

Answer 2

 to understand the functionality of the system and
 models are used to communicate with customers.
System Modeling

Question 3

Describe UML and its main usage

Answer 3

 Systems analysts use UML to describe O-O systems
 UML uses a set of symbols to represent graphically the various components and relationships within a system
 Although the UML can be used for business process modeling and requirements modeling, it is mainly
used to support O-O system analysis and to develop object models

Question 4

What are the different reasons why one would make models for existing and planned systems

Answer 4

 Models of the existing system are used during requirements engineering:
-They help clarify what the existing system does and can be
-Used as a basis for discussing its strengths and weaknesses.
-These then lead to requirements for the new system.

 Models of the new system are used during requirements engineering to help explain the proposed requirements to other system stakeholders.
-Engineers use these models to discuss design proposals and to document the system for implementation.
 In a model-driven engineering process, it is

Question 5

What is the importance of models in model-driven engineering processes

Answer 5

In a model-driven engineering process, it is possible to generate a complete or partial system implementation from the system model.

Question 6

Describe the different system perspectives

Answer 6

 An external perspective, where you model the context or environment of the system. (For example DFDs, Context Diagrams)
 An interaction perspective, where you model the interactions between a system and its environment, or between the components of a system. (For example ERDs)
 A structural perspective, where you model the organization of a system or the structure of the data that is processed by the system. (For example Object Relationship Diagrams)
 A behavioral perspective, where you model the dynamic behavior of the system and how it responds to events. (For example Use cases, Sequence Diagram, Activity Diagrams etc)

Question 7

Describe a DFD

Answer 7

 A data flow diagram (DFD) uses various symbols to
show how the system transforms input data into useful
information
 A DFD shows how data moves through an information system but does not show program logic or processing steps.
 A set of DFDs provide a logical model that shows what the system does, not how it does it

Question 8

What symbol set do we use for DFD symbols?

Answer 8

Gane and Sarson symbol set

Question 9

What are some points to note

Answer 9

-EVERYTHING is all caps
-SINGULAR is for everything except data stores

Question 10

Describe and illustrate the DFDs symbols

Answer 10

-process- receives input data and produces output eg APPLY RENT
-data flow- data path. eg DEPOSIT
-data store- data that the system stores because some processes need to use the data at a later time eg STUDENTS
-external entity/terminator- shows the boundaries of the system and how the system interfaces with the outside world

*See notes for illustration

Question 11

Give example of errors that may occur when using data flow symbols

Answer 11

Spontaneous generation- 2 outputs no input
Black hole- 2 inputs no output
Gray hole- input doesn’t make sense eg DOB to calculate grade

Question 12

What are some rules regarding the use of data store symbols

Answer 12

 A data store MUST be connected to a process with a data flow. Can’t be connected to another data store or an external entity
 The data store has at least one incoming and one
outgoing data flow and is connected to a process symbol with a data flow Cannot be connected to another entity or to a data store

Question 13

What is a context diagram

Answer 13

A context diagram is a top-level view of an information system that shows the system’s boundaries and scope
*Does not have data stores

Question 14

What is a functional primitive

Answer 14

It is a process that consists of a single function that is
not exploded further

Question 15

Describe leveling

Answer 15

Leveling/exploding/partitioning/decomposing
It is the process of drawing a series of increasingly
detailed diagrams, until all functional primitives are identified

Question 16

Describe balancing

Answer 16

It maintains consistency on parent and child DFDs by
ensuring that input and output data flows align
properly

Question 17

Describe the data dictionary and what an analyst could use it for

Answer 17

 This is a central storehouse of information about the system’s data that defines and describes all data elements and meaningful combinations of data elements
 An analyst uses the data dictionary to collect,
document, and organize specific facts about the system, including the contents of data flows, data stores, entities, and processes

Question 18

What is a data element and what is a data dictionary?

Answer 18

 A data element/ a data item/ field is the smallest piece of data that has meaning within an information system
 A record is a meaningful combination of related data elements that is included in a data flow or retained in a data score