An Excursion into Government Legacy IT Systems - VII

7.     Requirements

This chapter is devoted to explaining the types of requirements and constraints which will be levied on the systems.

7.1     Functional Requirements

Functional requirements describe what the systems will do. They start with activities, what the users will do. The baseline for functional requirements will come, as expected, from the legacy systems. These steps apply to defining activities:

·         Define activities in close cooperation agency-system users, because they know their jobs, and (where applicable) the public;

·         Cover legacy activities because the new system cannot be less capable than the legacy system;

·         Add new activities as needed; and

·         Assure upward compatibility (continued support) of activities.

Functions are what systems do to carry out activities. For example, to implement an activity such as display employee record, a system might have to verify an access permission, locate the employee object, verify identifying data, retrieve the record in question, and package the data for display to the user. In general,

·         Activities will request functions across the Layer/Layer interface,

·         Functions will build (within a layer) on Objects, and

·         The system will cover legacy functions (immediately through interfaces).

7.2     System Quality Requirements

Quality requirements establish how well the system must perform activities and functions. Examples of quality requirements are

·         Speed of operation / latency

·         System availability

·         System scalability

·         Data and design consistency across agencies

·         Ease of system use to facilitate training, reduce operator errors, and upgrade user productivity.

·         Security, which includes object privacy, encryption, authorization, authentication, and access permissions,

·         Integrity, which may be transaction-based (as for financial systems) and

·         System and data survivability, enabled by redundancy

7.3     Constraints

In general, constraints have important but indirect influence on system development and operation. Constraints will include

·         Costs

·         Schedules

·         Physical aspects such as size, weight, power use, etc.

·         Documentation and model standards and

·         On-line help