"PRIDE"-Information Systems Engineering Methodology (ISEM)

PRIDE

-ISEM

Information Systems Engineering Methodology
PHASE 2 - SYSTEM DESIGN
ACTIVITY B - DEFINE SUB-SYSTEM LOGIC

EXAMPLES TOOLS & TECHNIQUES FUNCTIONAL MATRIX CHECKLIST SUPPORT FORMS

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CONTENTS

This section contains the following:

BUSINESS PURPOSE

OVERVIEW

STEPS IN EXECUTION

SUPPLEMENTAL INFORMATION (separate sections)
- Phase 2 Review Checklist

BUSINESS PURPOSE

The purpose of this activity is to complete the specifications for each sub-system.

OVERVIEW

Systems Engineering updates the System Logic Narrative to support of the Systems Flowchart. The narrative should contain text describing: the Business Purpose of the system, what type of information requirements are implemented, who will use the system, and any special implementation considerations.

The "application logical" files are completed and text added to the FD's to describe each "object."

The relationship between inputs, outputs and files need to be explicitly defined. Within a single sub-system, there may be many inputs, many outputs, and many logical files. These relationships must be explicitly defined for control purposes. For example:

On the Input Description, define all of the outputs triggered by the input.

ID ------> OD

On the Input Description, define all subordinate inputs. This is particularly useful for tracking subordinate screens and windows in an interactive sub-system.

ID ------> ID

For inputs used to collect data in file maintenance sub-systems, define the files where data will be stored.

ID ------> FD

On the Output Description, define the application logical files containing the data used to support the output.

OD ------> FD

These relationships will be particularly useful in the future when performing an "impact analysis."

During this activity, Systems Engineering takes the opportunity to reappraise the rough design of the system. Although each sub-system is being finalized in Phase 2, the procedures and programs are re-evaluated. This will be needed to update the Project Plan and project estimates/schedules.

A Sub-System Concept Diagram is prepared for each sub-system. Like the System Concept Diagram used in Phase 1, the Sub-System Concept Diagram is a free-form schematic which depicts the anticipated processing flow for the sub-system. The graphic is supported by Sub-System Logic Narrative which provides a textual explanation of:

The Business Purpose of the sub-system.
Steps in Execution.
Special processing rules.
Implementation considerations.

PURCHASED PACKAGE CONSIDERATIONS

For those sub-systems implemented by a purchased package, text should be provided in the Sub-System Logic Narrative that mentions how the package is used in the sub-system. Also, inputs, outputs and files should be documented accordingly.

DELIVERABLES

The deliverables resulting from this activity include:

Updated System Logic Narrative.
Application Logical Files Discussion.
Sub-System Concept Diagram.
Sub-System Logic Narrative.e

STEPS IN EXECUTION

Systems Engineering updates the System Logic Narrative. The narrative describes the overall system, the types of information requirements implemented, and the business functions involved (user departments).

Systems Engineering prepares the Application Logical Files Discussion. This is narrative describing each "object" used in the system.

Systems Engineering establishes relationships between inputs, outputs, and files.

Systems Engineering reviews the remaining rough design (procedures and programs) and update the design as required.

Systems Engineering prepares a Sub-System Concept Diagram for each sub-system, along with Sub-System Logic Narrative.