Identify use cases, external and temporal business events for a system.

1
Lesson-22 Process Modeling(2)

• 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.
• Document the distribution of processes to
  locations.
• Synchronize data and process models using a CRUD
  matrix.

2
Data Types and Domains

• Data attributes should be defined by data types
  and domains.
• A data type defines what class of data can be
  stored in an attribute (e.g., character,
  integers, real numbers, dates, pictures, etc.).
• A domain defines what values or range of values
  an attribute can legitimately take on.

3
Diverging and Converging Data Flows

• A diverging data flow is one that splits into
  multiple data flows.
• Useful for illustrating data that starts out
  naturally as one flow, but needs to be routed to
  parallel processes.
• Also useful for illustrating multiple copies of
  the same output going to different destinations.
• A converging data flow is the merger of multiple
  data flows into a single packet.
• Useful for illustrating data from multiple
  sources that must come back together for some
  subsequent processing

4
Diverging and Converging Data Flows
5
External Agents

• An external 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.
• External agents define the boundary or scope of
  a system being modeled.
• 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 your systems end-users or managers

6
Data Stores

• A data store is an inventory of data.
• Frequently implemented as a file or database.
• A data store is data at rest compared to a data
  flow that is data in motion.
• Almost always one of the following
• Persons (or groups of persons)
• Places
• Objects
• Events (about which data is captured)
• Concepts (about which data is important)
• Data stores depicted on a DFD store all instances
  of data entities (depicted on an ERD)

7
When to Draw Process Models

• Strategic systems planning
• Enterprise process models illustrate important
  business functions.
• Business process redesign
• As is process models facilitate critical
  analysis.
• To be process models facilitate improvement.
• Systems analysis (primary focus of this course)
• Model the existing system including its
  limitations
• Model the target systems logical requirements
  (meaning processes and data flows needed
  regardless of how the system will be implemented)
• Model candidate technical solutions (physical
  DFDs only)
• Model the target technical solution (physical
  DFDs only)

8
Classical Structured Analysis

• Draw top-down physical DFDs that represent the
  current physical implementation of the system
  including its limitations.
• Convert the physical DFDs to their logical
  equivalents.
• Draw top-down logical DFDs that represent an
  improved system.
• Describe all data flows, data stores, policies,
  and procedures in a data dictionary or
  encyclopedia.
• Optionally, mark up copies of the logical DFDs to
  represent alternative physical solutions.
• Draw top-down physical DFDs that represent the
  target solution.
• THE ABOVE METHODOLOGY IS RARELY PRACTICED
  ANYMORE BECAUSE IT IS VERY CUMBERSOME AND
  TIME-CONSUMING.

9
Modern Structured Analysis

• Draw a context DFD to establish initial project
  scope.
• Draw a functional decomposition diagram to
  partition the system into subsystems.
• Create an event-response or use-case list for the
  system to define events for which the system must
  have a response.
• Draw an event DFD (or event handler) for each
  event.
• Merge event DFDs into a system diagram (or, for
  larger systems, subsystem diagrams).
• Draw detailed, primitive DFDs for the more
  complex event handlers.
• Document data flows and processes in the data
  dictionary.
• THE ABOVE METHODOLOGY, BASED ON EVENT
  PARTITIONING, IS MORE COMMONLY PRACTICED.

10
Structured Analysis Diagram Progression
11
CASE for DFDs (Sample Screen)
12
Events

• Events define processes needed to respond to
  those events.
• External events are those initiated by external
  agents. They result in an input transaction or
  data flow.
• Temporal events are those that are triggered by
  the passage of time. They simply happen and
  are indicated by a control flow.
• State events are those based on a systems change
  from one state to another.

13
Use Cases

• Use cases are based upon object-oriented concepts
  that are essentially the same as events.
• Use case analysis is the process of identifying
  and modeling business events and how the system
  responds to them.
• An actor is anything that needs to interact with
  the system (essentially, a synonym for external
  agent).

14
Use Case List
Actor
Event (or Use Case)
Trigger
Responses




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Establishes a new
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Marketing

Establishes
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RESUBSCRIPTION PROGR
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Marketing

Changes a subscription plan
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.

CHANGE
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extending the
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A subscription plan expires.
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CHANGE CONFIRMATION
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15
System DFD (see book for more readable copy)
16
Data to Process CRUD Matrix
17
Process to Location Association Matrix