6 Systems Analysis and Design in a Changing World, Fourth Edition

6 Systems Analysis and Design in a Changing World, 4th Edition 2

6 3 Learning Objectives u Explain how the traditional approach and the object-oriented approach differ when modeling the details of a use case u List the components of a traditional system and the symbols representing them on a data flow diagram u Describe how data flow diagrams can show the system at various levels of abstraction

6 Systems Analysis and Design in a Changing World, 4th Edition 4 Learning Objectives ( continued ) u Develop data flow diagrams, data element definitions, data store definitions, and process descriptions u Read and interpret Information Engineering models that can be incorporated within traditional structured analysis u Develop tables to show the distribution of processing and data access across system locations

6 Systems Analysis and Design in a Changing World, 4th Edition 5 Overview u What the system does and what event occurs – activities and interactions (use case) u Traditional structured approach to representing activities and interactions u Diagrams and other models of the traditional approach u RMO customer support system example shows how each model is related u How traditional and IE approaches and models can be used together to describe system

6 Systems Analysis and Design in a Changing World, 4th Edition 6 Traditional versus Object-Oriented Approaches

6 Systems Analysis and Design in a Changing World, 4th Edition 7 Traditional Approach in this Chapter

6 Systems Analysis and Design in a Changing World, 4th Edition 8 Data Flow Diagrams (DFDs) u Graphical system model that shows all main requirements for an IS in one diagram l Inputs/outputs l Processes l Data storage u Easy to read and understand with minimal training

6 Systems Analysis and Design in a Changing World, 4th Edition 9 Data Flow Diagram Symbols (Figure 6-3)

6 Systems Analysis and Design in a Changing World, 4th Edition 10 DFD Fragment Showing Use Case Look up item availability from the RMO (Figure 6-4)

6 Systems Analysis and Design in a Changing World, 4th Edition 11 DFD Integrates Event Table and ERD (Figure 6-5)

6 Systems Analysis and Design in a Changing World, 4th Edition 12 DFD Integrates Event Table and ERD

6 Systems Analysis and Design in a Changing World, 4th Edition 13 DFD and Levels of Abstraction u Data flow diagrams (DFDs) are decomposed into additional diagrams to provide multiple levels of detail u Higher-level diagrams provide general views of system u Lower-level diagrams provide detailed views of system u Differing views are called levels of abstraction

6 Systems Analysis and Design in a Changing World, 4th Edition 14 Layers of DFD Abstraction for Course Registration System (Figure 6-6)

6 Systems Analysis and Design in a Changing World, 4th Edition 15 Context Diagrams u DFD that summarizes all processing activity for the system or subsystem u Highest level (most abstract) view of system u Shows system boundaries u System scope is represented by a single process, external agents, and all data flows into and out of the system

6 Systems Analysis and Design in a Changing World, 4th Edition 16 DFD Fragments u Created for each use case in the event table u Represent system response to one event within a single process symbol u Self-contained models u Focus attention on single part of system u Show only data stores required in the use case

6 Systems Analysis and Design in a Changing World, 4th Edition 17 Three Separate DFD Fragments for Course Registration System

6 Systems Analysis and Design in a Changing World, 4th Edition 18 Event-Partitioned System Model u DFD to model system requirements using single process for each use case/activity in system or subsystem u Combines all DFD fragments together to show decomposition of the context-level diagram u Sometimes called “diagram 0” u Used primarily as a presentation tool u Decomposed into more detailed DFD fragments

6 Systems Analysis and Design in a Changing World, 4th Edition 19 DFD Fragments for Course Registration System

6 Systems Analysis and Design in a Changing World, 4th Edition 20 Combining DFD Fragments to Create Event- Partitioned System Model (Figure 6-8)

6 Systems Analysis and Design in a Changing World, 4th Edition 21 Context Diagram for RMO Customer Support System (Figure 6-9)

6 Systems Analysis and Design in a Changing World, 4th Edition 22 RMO Subsystems and Use Cases/Activities from Event Table (Figure 6-10)

6 Systems Analysis and Design in a Changing World, 4th Edition 23 RMO Activity-Data Matrix (CRUD) (Figure 6-39)

6 Systems Analysis and Design in a Changing World, 4th Edition 24 Context Diagram for RMO Order-Entry Subsystem (Figure 6-11)

6 Systems Analysis and Design in a Changing World, 4th Edition 25 Five Separate DFD Fragments for RMO Order-Entry Subsystem (Figure 6-12)

6 Systems Analysis and Design in a Changing World, 4th Edition 26 Decomposing DFD Fragments u Most DFD fragments can be further described using structured English u Sometimes DFD fragments need to be diagrammed in more detail u Decomposed into subprocesses in a detailed DFD u DFD numbering scheme l Hierarchical decomposition u DFD Fragment 2 is decomposed into Diagram 2 u Diagram 2 has processes 2.1, 2.2, 2.3, 2.4

6 Systems Analysis and Design in a Changing World, 4th Edition 27 Detailed DFD for Create new order DFD Fragment (Figure 6-14)

6 Systems Analysis and Design in a Changing World, 4th Edition 28 Physical and Logical DFDs u Logical model l Assumes implementation in perfect technology l Does not tell how system is implemented u Physical model l Describes assumptions about implementation technology l Developed in last stages of analysis or in early design

6 Systems Analysis and Design in a Changing World, 4th Edition 29 Physical DFD for Scheduling Courses (Figure 6-15)

6 Systems Analysis and Design in a Changing World, 4th Edition 30 Evaluating DFD Quality u Readable u Internally consistent and balanced u Accurately represents system requirements u Reduces information overload – rule of 7 +/- 2 l Single DFD should not have more than 7 +/-2 processes l No more than 7 +/- 2 data flows should enter or leave a process or data store in a single DFD u Minimizes required number of interfaces

6 Systems Analysis and Design in a Changing World, 4th Edition 31 Data Flow Consistency Problems u Differences in data flow content between a process and its process decomposition u Data outflows without corresponding inflows u Data inflows without corresponding outflows u Results in unbalanced DFDs

6 Systems Analysis and Design in a Changing World, 4th Edition 32 Consistency Rules u All data that flows into a process must l Flow out of the process, or l Be used to generate data that flows out of the process u All data that flows out of a process must l Have flowed into the process, or l Have been generated from data that flowed into the process

6 Systems Analysis and Design in a Changing World, 4th Edition 33 Unnecessary Data Input: Black Hole

6 Systems Analysis and Design in a Changing World, 4th Edition 34 Process with Impossible Data Output: Miracle Should be 

6 Systems Analysis and Design in a Changing World, 4th Edition 35 Process with Unnecessary Data Input (Figure 6-18)

6 Systems Analysis and Design in a Changing World, 4th Edition 36 Process with Impossible Data Output (Figure 6-19)

6 Systems Analysis and Design in a Changing World, 4th Edition 37 Documentation of DFD Components u Lowest-level processes need to be described in detail u Data flow contents need to be described u Data stores need to be described in terms of data elements u Each data element needs to be described u Various options for process definition exist

6 Systems Analysis and Design in a Changing World, 4th Edition 38 Structured English u Method of writing process specifications u Combines structured programming techniques with narrative English u Well-suited for lengthy sequential processes or simple control logic (single loop or if-then-else) u Ill-suited for complex decision logic or few (or no) sequential processing steps

6 Systems Analysis and Design in a Changing World, 4th Edition 39 Structured English Example (Figure 6-20)

6 Systems Analysis and Design in a Changing World, 4th Edition 40 Process 2.1 and Structured English Process Description (Figure 6-21)

6 Systems Analysis and Design in a Changing World, 4th Edition 41 Decision Tables and Decision Trees u Can summarize complex decision logic better than structured English u Incorporate logic into the table or tree structure to make descriptions more readable

6 Systems Analysis and Design in a Changing World, 4th Edition 42 Decision Tree for Calculating Shipping Charges (Figure 6-24)

6 Systems Analysis and Design in a Changing World, 4th Edition 43 Data Flow Definitions u Textual description of data flow’s content and internal structure u Often coincide with attributes of data entities included in ERD plus computed values u Algebraic notion describes data elements on data flow plus data structure

6 Systems Analysis and Design in a Changing World, 4th Edition 44 Data Flow Definition for RMO Products and Items Control Break Report (Figure 6-29)

6 Systems Analysis and Design in a Changing World, 4th Edition 45 Data Element Definitions u Data type description l String, integer, floating point, Boolean l Sometimes very specific written description u Length of element u Maximum and minimum values u Data dictionary – repository for definitions of data flows, data stores, and data elements

6 Systems Analysis and Design in a Changing World, 4th Edition 46 Data Element Definition Examples (Figure 6-30)

6 Systems Analysis and Design in a Changing World, 4th Edition 47 Components of a Traditional Analysis Model (Figure 6-31)

6 Systems Analysis and Design in a Changing World, 4th Edition 48 Information Engineering Models u Focus on strategic planning, enterprise applications, and data requirements of new system u Share features with structured system development methodology u Developed by James Martin in early 1980’s u Thought to be more rigorous and complete than the structured approach

6 Systems Analysis and Design in a Changing World, 4th Edition 49 Information Engineering System Development Life Cycle Phases ISP BAA BSD Construction

6 Systems Analysis and Design in a Changing World, 4th Edition 50 Process Decomposition and Dependency Models u IE process models show three information types l Decomposition of processes into other processes l Dependency relationships among processes l Internal processing logic u Process decomposition diagram – represents hierarchical relationship among processes at different levels of abstraction u Process dependency model – describes ordering of processes and interaction with stored entities

6 Systems Analysis and Design in a Changing World, 4th Edition 51 Process Decomposition Diagram for RMO (Figure 6-34)

6 Systems Analysis and Design in a Changing World, 4th Edition 52 Process Dependency Diagram (Figure 6-35)

6 Systems Analysis and Design in a Changing World, 4th Edition 53 Locations and Communication Through Networks u Logical information needed during analysis l Number of user locations l Processing and data access requirements at various locations l Volume and timing of processing and data access requests u Needed to make initial design decisions such as l Distribution of computer systems, application software, database components, network capacity

6 Systems Analysis and Design in a Changing World, 4th Edition 54 Gathering Location Information u Identify locations where work is to be performed u Draw location diagram u List functions performed by users at each location u Build activity-location matrix l Rows are system activities from event table l Columns are physical locations u Build activity-data (CRUD) matrix l CRUD – create, read, update, and delete

6 Systems Analysis and Design in a Changing World, 4th Edition 55 RMO Activity-Location Matrix (Figure 6-38)

6 Systems Analysis and Design in a Changing World, 4th Edition 56 RMO Activity-Data Matrix (CRUD) (Figure 6-39)

6 Systems Analysis and Design in a Changing World, 4th Edition 57 Summary u Data flow diagrams (DFDs) are used in combination with event table and entity-relationship diagram (ERD) to model system requirements u DFDs model system as set of processes, data flows, external agents, and data stores u DFDs easy to read – graphically represent key features of system using small set of symbols u Many types of DFDs – context diagrams, DFD fragments, subsystem DFDs, event-partitioned DFDs, and detailed process DFDs

6 Systems Analysis and Design in a Changing World, 4th Edition 58 Summary ( continued ) u Each process, data flow, and data store requires detailed definition u Analyst may define processes as structured English process specifications, decision tables, decision trees, or detail process DFDs u Detailed process decomposition DFDs used when internal process complexity is great u Data flows are defined by component data elements and their internal structure (algebraic notation)

6 Systems Analysis and Design in a Changing World, 4th Edition 59 Summary ( continued ) u Models from IE may supplement DFDs l Process decomposition diagram (how processes on multiple DFD levels are related) l Process dependency diagram (emphasizes interaction with stored entities) l Location diagram (where system is used) l Activity-location matrix (which processes are implemented at which locations) l Activity-data (or CRUD) matrix (where data is used)