Modeling. Slides by: Ms. Shree Jaswal. Slides by:ms. Shree Jaswal 1

Transcription

1 Modeling Slides by: Ms. Shree Jaswal Slides by:ms. Shree Jaswal 1

2 Model What is a model? a model is a simplification of reality Why do we model? we build models so that we can better understand the system we are developing we build models of complex systems because we cannot comprehend such a system in its entirety four aims to achieve help us to visualize a system permit us to specify the structure/behavior of a system give us a template that guides us in constructing systems document the decisions we have made Slides by:ms. Shree Jaswal 2 Chapter 7 Slides by:ms. Shree Jani

3 Objectives of Analysis Model Objectives of analysis model To describe what the customer require To establish a basis for the creation of a software design To define a set of requirements that can be validated once the software is built Slides by:ms. Shree Jaswal 3

4 A Bridge system de sc ription analysis model design model Slides by:ms. Shree Jaswal 4

5 Analysis Model Data Object description Data ERD Data dictionary Function DFD Process specification (PSPEC) STD Behavior Control Specification (CSPEC) Slides by:ms. Shree Jaswal 5

6 Data Modeling: ER Diagram Examines data objects independently of processing Focuses attention on the data domain Creates a model at the customer s level of abstraction Indicates how data objects relate to one another Slides by:ms. Shree Jaswal 6

7 ERD Notation One common form: object (0, m) relationship 1 object (1, 1) 2 Another common form: attribute object relationship 1 object 2 (0, m) (1, 1) Slides by:ms. Shree Jaswal 7

8 An Example Customer standard task table (1,1) selected from places (1,1) (1,m) (1,w) work tasks materials (1,w) (1,i) request for service (1,1) generates (1,n) consists of lists (1,1) work order (1,1) Slides by:ms. Shree Jaswal 8

9 Functional Modeling: Data Flow Diagram Every computer-based system is an information transform... input computer based system output Slides by:ms. Shree Jaswal 9

10 Notation external entity process data flow data store Slides by:ms. Shree Jaswal 10

11 External Entity A producer or consumer of data Example: person, device, system, sensor Data must always originate from somewhere, and must always be sent to something Slides by:ms. Shree Jaswal 11

12 Process A data transformer (changes input to output) Example: compute taxes, determine area, format report, display graph Data must always be process in some way to achieve system function Slides by:ms. Shree Jaswal 12

13 Data Flow Data flows through a system, beginning as input and be transformed into output base height compute triangle area area Slides by:ms. Shree Jaswal 13

14 Data Store Data is often stored for later use report required sensor # look-up sensor data sensor number sensor #, type, location, age type, location, age sensor data Slides by:ms. Shree Jaswal 14

15 Data Flow Diagramming: Guidelines all icons must be labeled with meaningful names the DFD evolves through a number of levels of detail always begin with a context level diagram (also called level 0) always show external entities at level 0 always label data flow arrows do not represent procedural logic Slides by:ms. Shree Jaswal 15

16 Constructing a DFD I review the data model to isolate data objects and use a grammatical parse to determine operations determine external entities (producers and consumers of data) create a level 0 DFD Slides by:ms. Shree Jaswal 16

17 Level 0 user video source processing request NTSC video signal digital video processor requested video signal monitor Slides by:ms. Shree Jaswal 17

18 Example: Level 0 Slides by:ms. Shree Jaswal 18

19 Constructing a DFD II write a narrative describing the transform parse to determine next level transforms balance the flow to maintain data flow continuity develop a level 1 DFD use a 1:5 (approx.) expansion ratio Slides by:ms. Shree Jaswal 19

20 Level 1 x a P b y level 0 a p1 c p2 f d level 1 p3 e p4 5 g b Slides by:ms. Shree Jaswal 20

21 Example: Level 1 Slides by:ms. Shree Jaswal 21

22 Example : Level 2 Slides by:ms. Shree Jaswal 22

23 Flow Modeling Notes Each bubble is refined until it does just one thing The expansion ratio decreases as the number of levels increase Most systems require between 3 and 7 levels for an adequate flow model Slides by:ms. Shree Jaswal 23

24 Behavioral Modeling events behavior Outside world Application How do I model the software's reaction to some external event? Slides by:ms. Shree Jaswal 24

25 The States of a System state a set of observable circum-stances that characterizes the behavior of a system at a given time state transition the movement from one state to another event an occurrence that causes the system to exhibit some predictable form of behavior action process that occurs as a consequence of making a transition Slides by:ms. Shree Jaswal 25

26 Behavioral Modeling make a list of the different states of a system (How does the system behave?) indicate how the system makes a transition from one state to another (How does the system change state?) indicate event indicate action draw a state diagram or a sequence diagram Slides by:ms. Shree Jaswal 26

27 Example full and start invoke manage-copying reading operator commands copies done invoke read-op-input Idle invoke read-op-input full invoke read-op-input making copies reloading paper empty invoke reload paper jammed invoke problem-diagnosis problem state not jammed invoke read-op-input Slides by:ms. Shree Jaswal 27

28 Statechart Diagram 28

29 System behaviour modelling with Sequence Diagram A behavioural model shows the interactions between objects to produce some particular system behaviour that is specified as a usecase Sequence diagrams (or collaboration diagrams) in the UML are used to model interaction between objects Slides by:ms. Shree Jaswal 29

30 An Example: Issue of electronic items E c a t : C a ta l og : L ib ra ry Ite m L i b1 : N e t S e rve r : L ib ra ry U s e r L o ok up D i s pl ay Iss u e Iss u e li c e nc e A c c e p t li c e nc e C o m pre ss D e l iv e r Slides by:ms. Shree Jaswal 30

31 Sequence Diagram Scenario: Invalid Pin Number :Client :ATMMachin :Bank Insert ATM card() Request PIN() Enter PIN Number() Eject ATM Card() Verify PIN Number() Bad PIN Number() Display main screen() 31

32 Thank You! Slides by:ms. Shree Jaswal 32