IT532 - SYSTEMS ANALYSIS - CLASS 1
- An information system is a set of organized interacting
procedures, processors, and storage devices that work together to
support the operations, management, and planning needs of an organization.
- A system exists in an environment.
There is a boundary that encloses the components and
separates them from the environment.
- A closed system does not interact with its environment.
It is difficult to find examples of pure closed systems.
- An open system interacts with its environment.
An information system is an open system.
- An information system interacts with actors.
An actor is an abstraction that represents any role that a system in
the environment can play during an interaction with our system.
- Information system interactions are client/server
The scope of our system is defined by the list of services that
it provides to its clients.
- A client interaction is initiated when an
actor requests a service that our system can perform.
Our system plays the server role in this type of interaction.
- A server interaction is initiated when our
system delegates work to an actor.
Our system plays the client role in this type of interaction.
- An input interface must be able to receive and
validate a client request or a server response when it arrives at the
boundary of our system.
- An output interface must be able to format and
transmit our response to a client or our request to a server.
- The system must be aware of its current state.
State is a memory which contains a history of prior interactions
so that a proper response can be generated for a current interaction.
- An event is something that takes place in the environment
of our system that is of interest to our system.
- An event may be a request for service from a client or it
may be a response to a request that our system made to a server.
The list of events that request services define the scope of
- A system detects that an event has occurred when a
stimulus that is generated by or on behalf of
an actor arrives at the boundary of the system.
- A stimulus may contain attributes (data flow) or it may be
a predetermined absolute or relative moment in time (temporal).
- There must be at least one response to each event.
The response may be to update the system state
or to send a message to an actor.
- A validation rule is a business policy
or constraint that is applied to an incomming stimulus to ensure
that it is authentic and valid.
- A transformation rule is a business policy
that is applied when the stimulus is mapped into a response.
- An essential event is an
event that is based on the
assumption of perfect technology.
A practical event is an
event that is based on the fact
that it will be processed using specific technologies.
- A requirement is any function, constraint or property
that the system must provide, meet, or satisfy to fulfill its purpose.
- A functional requirement is a function
that the system must perform.
- A non-functional requirement is a
characteristic or constraint that might limit our choice of
technology when we implement one or more
- A technology specification is a
constraint that dictates or mandates the way that a requirement
must be met.
- A requirement may also be categorized by its
priority and its expected
- The set of requirements for a system should be
- A true requirement is a feature or capability
that a system must possess in order to fulfill its purpose,
regardless of how it is implemented.
- A false requirement is a feature or capability
that is clearly irrelevant to the purpose of the system or
is an activity that must be carried out solely to accomodate
the technology that is used to implement the system.
- The essential functional requirements for an
information system is the set of
essential events that the system must
detect and process.
The essential requirements, which are true requirements,
are an ouput of the analysis process.
- The practical functional requirements for an
information system is the set of
practical events that are derived when specific
technologies are used to implement the
The practical requirements, which are usually
false requirements, are an ouput of the design process.
Prepared by David L. March -- Last Revised on August 16, 2001
COPYRIGHT © 1998-2001 BY DAVID L. MARCH