Chapter 9 Process Modeling Yong Choi BPA CSUB

Chapter 9 Process Modeling Yong Choi BPA CSUB 1

Not to be discussed… • Structured English – No programming background…. does not make sense • Decision table – Operations management course…. • Data and Model synchronization – Will take at least 4 weeks… • Details of lower than DFD level 0 or 1 – Simple taste of DFDs will be enough this time…. – Can take up to a month to taste more of DFDs… 2

Chapter Nine Process Modeling • • • Define systems modeling and differentiate between logical and physical system models. Define process modeling and explain its benefits. Recognize and understand the basic concepts and constructs of a process model. Explain when to construct process models and where to store them. Construct a context diagram to illustrate a system’s interfaces with its work environment. Identify use cases, external and temporal business events for a system. Perform event partitioning and organize events in a functional decomposition diagram. Draw event diagrams and merge those events into a system diagram. 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. 3

Chapter Map 4

System Concept • A system exits by taking input from the environment , transforming (processing) input, and release an output • A system may be decomposed (exploded) into subsystems • Output of one subsystem may become the input of other subsystems 5

System Concept (con’dt) 6

System Decomposition (General) 7

Decomposition Diagram (Hierarchy Chart) 8

Example of Decomposition Diagram Sound. Stage Entertainment Club 9

Decomposition: se-Case Diagram 10

Separating data and processes • Characteristic u Process-orientation v Data-orientation • System focus u • Design stability u what, when & how to do Limited due to change in business processes v Operation of Data v More stable as data needs change slowly • Data organization u Designed for individual applications v Designed for enterprise u unstructured v Controlled • State of data 11

Separating data and processes • Process-oriented approach – An IS development strategy that focuses on how and when data are moved through and transformed by an IS – Sequence of steps in the process-oriented approach: • define problem -> identify necessary decisions -> describe information needs -> determine necessary processing -> specify data needs • Data-oriented approach – An IS development strategy that focuses on the optimal organization of data, not on where or how data are used – Sequence of steps in the data-oriented approach: • define problem -> identify requirements -> develop data model for each user's data -> integrate all the data models into an overall model 12

Data Flow Diagrams (DFD) • Key points for modeling – How data moves through the organization – Relationships between various data flows – Storage of data • Diagrams also called Process Models 13

Process Modeling with DFD Process Modeling is a technique for organizing and documenting the structure and flow of data through a system’s processes, and the logic, policies, and procedures to be implemented by a system’s processes. A Data Flow Diagram (DFD) is a graphical modeling tool to depict the flow of data through a system and the work or processing performed by that system. – What’s the system doing 14

Simple Data Flow Diagram for Banking 15

Process Logic • DFDs are effective tools for identifying processes, but are not good at showing all the detail logic inside those processes. – Not always easy to know what the lowest logical level is • However, it is better than: – Flowcharts and Pseudocode (difficult for users to understand). 16

Flowchart 17

Flowchart Limitations • Complex logic: Sometimes, the program logic is quite complicated. In that case, flowchart becomes complex and clumsy. • Alterations and Modifications: If alterations are required the flowchart may require re-drawing completely. • Reproduction: As the flowchart symbols cannot be typed, reproduction of flowchart becomes a problem. • The essentials of what is done can easily be lost in the technical details of how it is done. 18

Pseudocode • This is the pseudocode for a Game of Monopoly, including one person's move as a procedure: Main Procedure Monopoly_Game Hand out each player's initial money. Decide which player goes first. Repeat Call Procedure Monopoly_Move for next player. Decide if this player must drop out. Until all players except one have dropped out. Declare the surviving player to be the winner. Procedure Monopoly_Move Begin one's move. Throw the dice. Move the number of spaces on the board shown on the dice. If the token landed on "Go to Jail, " then go there immediately. Else if the token landed on "Chance" or "Community Chest, " then draw a card and follow its instructions. Else follow the usual rules for the square (buying property, paying rent, collecting $200 for passing "Go", etc. ). End one's move. 19

Elements of a DFD DE MARCO & YOURDON NOTATIONS External Entity Data Flow Process Data Store 20

Elements of a DFD GANE & SARSON NOTATIONS (Textbook) External Entity Data Flow 3 Process Pay Bill AP Clerk Data Store 21

External Entities SUPPLIER • An External Entity is a provider (source) or receiver (sink) of data and information of the system • External agents define the “boundary” or “scope” of a system being modeled. 22

External Entities … • An external entity (agent) defines a person, organization unit, or other organization that lies outside of the scope of the project but that interacts with the system being studied. – As scope changes, external agents can become processes, and vice versa. – Almost always one of the following: • Office, department, division inside the business but outside the system scope. • An external organization or agency. • Another business or another information system. • One of system’s end-users or managers 23

Data Stores D 1 Accounts Receivable • A data store is an inventory of data. – A data store means “data at rest. ” – A data flow means “data in motion. ” 24

Data Stores … – Almost always one of the following: • • • Persons (or groups of persons): e. g. , customer Places: e. g, cash register Objects: e. g. , product Events (about which data is captured): e. g. , sales Concepts (about which data is important): e. g. , discount – Data stores depicted on a DFD store all instances of data entities (depicted on an ERD) 25

Data Flows DELIVERY SLIP • A Data Flow represents an input of data to a process, or the output of data from a process. – A data flow may also be used to represent the creation, reading, deletion, or updating of data in a “data store. ” – A composite data flow (packet) is a data flow that consists of other data flows. • A Data Flow does not represent a document or a physical good: it represents the exchange of information in the document or about the good 26

Processes 1 Pay Bill • A Process is a work or action performed on input data flow to produce an output data flow • Use a verb to label the action performed by the process (not the name of person or department who does it as in physical DFD) • A Process must have at least one input data flow and at least one output data flow. 27

How to find each one… • External Entities (EE) – people/organizations/things that supply information to or use information from the system • Processes (P) – actions/doing words/verbs • Data Flows (DF) – movement/exchange of information/data between external entities to processes, and processes to processes • Data Stores (DS) – store/record information/data 28

DFD using Use-Case • The actor that initiates the event – External entities • The use cases – Will be handled by a process • Inputs (or triggers) & outputs and responses – Will become a flow of data ** data store is a result of data flow. . thus, need naming creativity… ** 29

DFD Naming Guidelines • External Entity Noun • Data Flow Names of data • Process verb phrase – a system name – a subsystem name • Data Store Noun 30

Guidelines for Developing DFD 1. Develop a list of business activities – Similar to business rules of ERD 2. Create the Context Diagram (we know this) – shows external entities and data flows to and from the system: conceptual DFD 3. Create level 0 DFD (or Diagram 0 in textbook) – shows general processes at the highest level 4. Create level 1 DFD (or Child Diagram in textbook) – shows more detailed processes 31

DFD Guidelines (con’t) Narrative Context Diagram 0 DFD Diagram 1 DFDs Diagram n DFDs E-R Diagram Process Descriptions 32

Apply logical sequence of the system. . • A student (EE) sends in an application form (DF) containing their personal details, and their desired course • The university checks (P) that the course is available. • If the course is available the student is enrolled (P) in the course, and the university confirms (P) the enrolment by sending a confirmation letter (DF) that they are registered for the course to the student. • Or if the course is unavailable the student is sent a rejection letter (DF). 33

Context DFD Building Procedure • Identify the system and its boundaries (the context) • Identify external entities (providers, receivers of system info) • Identify external data flows (input, output) – However, NO DATA STORE !!! • Note: the whole system itself is a process (it receives input and transforms into output) 34

Decomposition of Context Diagram M 0 P Context Diagram N M Level-0 Diagram D 1 1 N 2 3 P Level-1 Diagram 35

Where to Begin Creating DFDs • Start with the data flow from an external entity and work forwards • Start with the data flow to an external entity and work backwards • Examine the data flows into or out of a data store • Examine data flows, entity connections and data stores associated with a particular process • Note fuzzy, ill-defined areas of the system for further clarification 36

Description of Each Level • Context Diagram: This is the highest level and represents the overall system and its interaction with its environment • Level 0 Diagram: This shows the major subsystems and their interactions • Level x Diagram: Shows the processes that make up each of the major subsystems • Level x. y Diagram: Shows detail of the above diagrams 37

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When to Stop • Each process is a single decision or calculation or a single database operation, such as retrieve, update, create, delete or read. • Each data store represents data about a single entity such as a customer, employee, product or order. • The system user does not care to see any more detail or when you and other analysts have dcoumented sufficient detail to do subsequesnt systems development tasks. • Every data flow does not need to be split further to show that different data are handled in different ways. • You believe that you have shown each business form or transaction, computer screen and report as a single data flow. • You believe there is a separate process for each choice on all lowest -level menu options for the system. 39

Level 0 Tips • Generally move from top to bottom, left to right • Minimize crossed lines • Iterate as needed – The DFD is often drawn many times before it is finished, even with very experienced systems analysts 40

Level 0 and 1 DFD Building Procedure • Level-0 DFD – Identify what is being done between each input and its corresponding output – Identify the processes – Identify external data flows between external entities and processes – Identify internal data flows between processes and data stores • Level-1 DFD’s – Sub-processes (primitive processes) of Level-0 processes 41

Tips for Level 1 and Below • Sources for inputs and outputs listed at higher level • List source and destination of data flows to processes and stores within each DFD • Depth of DFD depends on overall system complexity – Two processes generally don’t need lower level – More than seven processes become overly complex and difficult to read 42

Rules in DFD Building • Rule 1 : Use only DFD notations to avoid confusion • Rule 2 : Use an action VERB to label a process (because a process is an action !!!) 43

Rules in DFD Building. . . • Rule 3 : Must be one process associated with each data flow … M M 44

Detail Rules in DFD Building. . . • Rule 3 : Must be one process associated with each data flow … M N 45

Detail Rules in DFD Building. . . • Rule 3 : Must be one process associated with each data flow. 46

Detail Rules in DFD Building. . . • Rule 4 : Shaded corner must appear in ALL occurrences of a duplicated symbol in a same diagram CUSTOMER D 3 Accounts Receivable 47

Detail Rules in DFD Building. . . • Rule 5 : No process without output data flow (black hole !!!) 48

Detail Rules in DFD Building. . . • Rule 6 : No process without input data flow (miracle !!!) 49

Detail Rules in DFD Building. . . • Rule 7 : No need for routing (without transforming) a data flow with a process (non value-added activities !!!) Info A 50

Detail Rules in DFD Building. . . • Rule 8 : Identical input, output data flows for parent and child processes (but the child processes can have their own throughputs) – See the picture in next slide 51

Detail Rules in DFD Building. . . M P Context Diagram N M 1 N 2 3 P Level-0 Diagram 52

Detail Rules in DFD Building. . . • Rule 9 : Data flows cannot split by themselves 53

Detail Rules in DFD Building. . . • Rule 9 : Data flows cannot split … 54

Detail Rules in DFD Building. . . • Rule 10 : A data packet can combine many data elements being transmitted at the same time to the same destination 55

Detail Rules in DFD Building. . . • Rule 11 : Double-headed arrows are forbidden [in- flow (update) and out-flow (extract info) of a data store are different] 56

Common Process Errors on DFDs 57

Data to Process Matrix 58

Process to Location Association Matrix 59

Logical vs. Physical Models Logical models show WHAT a system is or does. They are independent of any technical implementation. Physical models show not only what a system is or does, but also HOW the system is (to be) physically and technically implemented. They reflect technology choices. 60