Systems analysis and design methods 7th whitten and benley chapter 06

Process Modeling Introduction  The chapter will address the following questions:        What is systems modeling and what is the difference between logical and physical system models? What is process modeling and what are its benefits? What are the basic concepts and constructs of a process model How you read and interpret a data flow diagram When in a project are process models constructed and where are they stored? How you construct a context diagram to illustrate a system’s interfaces with its environment? How you identify external and temporal business events for a system? Process Modeling Introduction  The chapter will address the following questions:    How you perform event partitioning and organize events in a functional decomposition diagram? How you draw event diagrams and then merge those event diagrams into a system diagram? How you draw primitive data flow diagrams, and describe the elementary data flows and processes in terms of data structures and procedural logic (Structured English and decision tables), respectively? Process Modeling An Introduction to System Modeling  System Models    System models play an important role in systems development Systems analysts or users constantly deal with unstructured problems One way to structure such problems is to draw models  A model is a representation of reality Just as a picture is worth a thousand words, most system models are pictorial representations of reality Process Modeling An Introduction to System Modeling  System Models  Models can be built for existing systems as a way to better understand those systems, or for proposed systems as a way to document business requirements or technical designs   Logical models show what a system ‘is’ or ‘does’ They are implementation-independent; that is, they depict the system independent of any technical implementation As such, logical models illustrate the essence of the system Popular synonyms include essential model, conceptual model, and business model Physical models show not only what a system ‘is’ or ‘does’, but also how the system is physically and technically implemented They are implementation-dependent because they reflect technology choices, and the limitations of those technology choices Synonyms include implementation model and technical model Process Modeling An Introduction to System Modeling  System Models  Systems analysts have long recognized the value of separating business and technical concerns  They use logical system models to depict business requirements  They use physical system models to depict technical designs Process Modeling An Introduction to System Modeling  System Models  Systems analysis activities tend to focus on the logical system models for the following reasons:  Logical models remove biases that are the result of the way the current system is implemented or the way that any one person thinks the system might be implemented  Logical models reduce the risk of missing business requirements because we are too preoccupied with technical details  Logical models allow us to communicate with end-users in non-technical or less technical languages Process Modeling An Introduction to System Modeling  System Models  What is Process Modeling?  Process modeling is a technique for organizing and documenting the structure and flow of data through a system’s PROCESSES and/or the logic, policies, and procedures to be implemented by a system’s PROCESSES  Process modeling originated in classical software engineering methods  A systems analysis process model consists of data flow diagrams (DFDs) • A data flow diagram (DFD) is a tool that depicts the flow of data through a system and the work or processing performed by that system Synonyms include bubble chart, transformation graph, and process model Process Modeling INFORMATION SYSTEMS FRAMEWORK FOCUS ON SYSTEM DATA FOCUS ON SYSTEM PROCESSES FOCUS ON SYSTEM INTERFACES FOCUS ON SYSTEM GEOGRAPHY Business Functions System Context Survey Phase (establish scope and project plan) Accoun ts R eceivable Database Marketing Credit SYSTEM OWNERS Advertising Custom er Sales (scope) O rder O rder Manag ement System P icking O rder Warehou se Study Phase Credit Vouch er Orders Cancellatio ns FAST Methodology Services Ba nk Decomposition Diagram (establish system improvement objectives) Context Diagram Business Processe rejected o rder Custo mers S Y S T E M A N A L Y S T S credit c usto mer number SYSTEM USERS o rder (requirements) o rder w ith valid pro ducts Validate v alid o rder c usto mer o rder witho ut valid c usto mer C heck credit Validate pro ducts Orders Definition Phase appro ved o rder pric es P ro duc ts appro ved o rder quantity i n sto ck Rel ease o rder picking ticket (establish and prioritize business system requirements) Data Flow Diagrams Reverse Engineering (optional) SYSTEM DESIGNERS (specification) SYSTEM BUILDERS (components) Database Technology Interface Technology Software (and Hardware) Technology Networking Telchnology Process Modeling Monthly Account Statements New or Modified Monthly Statement Bank Monthly Statement Prior Monthly Statement Reconcile Account Balances Transaction Bill Creditor Payment Account Balance Current Balance Pay a Bill Account Transactions Bank Accounts Modified Balance Payment Modified Balance Withdraw Funds from an Account Deposit Account Transactions Withdraw or transfer Employer Pay Bank Other Income Source Reimbursement Deposit Funds into an Account Process Modeling An Introduction to System Modeling  System Models  Data Flow Diagram  There are only three symbols and one connection: • The rounded rectangles represent processes or work to be done • The squares represent external agents – the boundary of the system • The open-ended boxes represent data stores, sometimes called files or databases, and correspond to all instances of a single entity in a data model • The arrows represent data flows, or inputs and outputs, to and from the processes 10 Process Modeling How to Construct Process Models  The Event Diagram  For each event, illustrate the following:  The input(s) and its source(s) • Sources are depicted as external agents • The data structure for the input should be recorded in the repository  The outputs and their destinations • Destinations are depicted as external agents • The data structure for the output should be recorded in the repository 86 Process Modeling How to Construct Process Models  The Event Diagram  For each event, illustrate the following: (continued)  Any data stores from which records must be ‘read’ should be added to the event diagram • Data flows should be added and named to reflect what data is read by the process  Any data stores in which records must be ‘created’, ‘deleted’, or ‘updated’ should be included in the event diagram • Data flows to the data stores should be named to reflect the nature of the update 87 Process Modeling Event Diagram Event: Member changes name or address P Member Name/Address Change Confirm Process Change of Address Change of Address 88 Update to Name/Address D Members Process Modeling Event Diagram Event : Member respo nds t o promo t io nal o rder D Original Dat ed Order Orders D Acco unt s Receivable DB Updat e t o Order St at us Updat e: Order Changes Credit Rat ing and Limit s Member P Member Order Respo nse Backo rder Pro cess Member Order Respo nse Wareho use Picking T icket Updat e t o Membership Credit s Pro duct Availabilit y D Memberships D Members D Updat e t o Agreement St at s D Member Address 89 Pro duct s Agreement s Process Modeling Event Diagram Event : Deadline f o r member t o repo snd t o dat ed o rder has passed D Original Dat ed Order Orders D Acco unt s Receivable DB Updat e t o Order St at us Updat e: Order Changes Credit Rat ing and Limit s P Deadline t o Fill Dat ed Order Aut o mat ically Fill Dat ed Order Wareho use Picking T icket Updat e t o Membership Credit s D Memberships D Members Pro duct Availabilit y Member Address D Updat e t o Agreement St at s D 90 Pro duct s Agreement s Process Modeling How to Construct Process Models  The Event Diagram   Each event process should be described to the CASE repository with the following properties:  Event sentence – for business perspective  Throughput requirements – the volume of inputs per some period of time  Response time requirements – how fast the typical event must be handled  Security, audit, and control requirements  Archival requirements (from a business perspective) All of the above properties can be added to the descriptions associated with the appropriate processes, data flows, and data stores on the model 91 Process Modeling How to Construct Process Models  The System Diagram     The system diagram is said to be ‘exploded’ from the single process that was created on the context diagram The system diagram(s) shows either:  all of the events for the system on a single diagram  all of the events for a single subsystem on a single diagram Depending on the size of the system, a single diagram may be too large Synchronization is the balancing of data flow diagrams at different levels of detail to preserve consistency and completeness of the models  Synchronization is a quality assurance technique 92 Process Modeling Figure 6-27 We are sorry but the diagram is currently not available Please refer to your textbook, pages 250 and 251 93 Process Modeling How to Construct Process Models  The System Diagram   The event diagram processes are merged into the system diagrams It is very important that each of the data flows, data stores, and external agents that were illustrated on the event diagrams be represented on the system diagrams  This is called balancing  Most CASE tools include facilities to check balancing for errors 94 Process Modeling How to Construct Process Models  The System Diagram   When creating a system diagram, not consolidate data stores – otherwise, you will create balancing errors between the system and event diagrams You may elect to consolidate some data flows (from event diagrams) into composite data flows on the system diagram  If you do, be sure to use junctions on the event diagrams to demonstrate how the elementary data flows are derived from the composite data flows 95 Process Modeling How to Construct Process Models  Primitive Diagrams    Each event process on the system diagram(s) must be exploded into either:  a procedural description  a primitive data flow diagram For event processes that are not very complex – in other words, they are both an event and an elementary process, they should be described in one page (usually much less) of Structured English Event processes with more complex event diagrams should be exploded into a more detailed, primitive data flow diagram 96 Process Modeling How to Construct Process Models  Primitive Diagrams   A primitive DFD shows detailed processing requirements for the event A primitive DFD shows several elementary processes for the event process  Each elementary process is cohesive – that is, it does only one thing  Each of the elementary processes can now be described with procedural Structured English specifications, and where appropriate, decision tables 97 Process Modeling Backorder Invalid Product ID Member Demographics P Invalid Member ID D Updated Member Demographics Validat e Member Original Dat ed Order Member ID and Address Members D Orders Update: Order Changes Updat e Order Product P Ordered Product ID D Ordered Products Check Ordered Product Validity Product ID Member Member Order Response Valid Product Product Availabilit yD Product s P Check Product Availabilit y Inventory Commit ment Updat e Ordered Product St at us Ordered Product Quant ity Available Product and Quant it y P Calculate Ext ended Cost Product Price Ordered Product Ext ended Price P P Check Member Credit Payment Met hod and Amount Total Order Price Calculat e Order Tot al Cost Pre-Payment Request Credit Rat ing and Limit s Fillable Ordered Product Fillable Order D Accounts Receivable DB Update t o Order St at us Warehouse P P Release Order Picking T icket to Warehouse D Member Address D Orders Members Element ary Processes f or Process Member Order Response R Mart inez as of March 6, 1997 Credit Member Purchase Updat e t o Membership Credit s D Memberships D Agreements Updated Act ivit y Record Update t o Agreement St at s 98 Process Modeling The Next Generation  The Next Generation   Process modeling skills remain valuable for two reasons:  The current interest of business process redesign requires process models  Process models are included in many object modeling strategies such as the Object Modeling Technique (OMT) Business process design emphasizes physical process modeling  Physical process models include those processes which reflect the current implementation • This may include sequential processes that merely edit, route, copy or approve a data flow • Physical data flow diagrams also include additional details such as who or what performs each process, the cost of each process, and a critical evaluation of the value returned by each process 99 Process Modeling Summary       Introduction An Introduction to System Modeling System Concepts for Process Modeling The Process of Logical Process Modeling How to Construct Process Models The Next Generation 100 ...    Systems thinking is the application of formal systems theory and concepts to systems problem solving Systems theory and concepts help us understand the way systems are organized, and how... understand when viewed as a whole (meaning, as a single process)? • In systems analysis we separate a system into its component subsystems, which in turn are decomposed into smaller subsystems,... Process modeling is a technique for organizing and documenting the structure and flow of data through a system’s PROCESSES and/ or the logic, policies, and procedures to be implemented by a system’s