Specifying Non-functional Requirements for Real-Time
Systems
Topic Area: Software requirements Engineering
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Satish Mahadevan Srinivasan,
College of Information Science and Technology, University of Nebraska at
Omaha, NE-68182
smsrinivasan@mail.unomaha.edu
Telephone No: 402-214-8226

Scott Lancaster,
College of Information Science and Technology, University of Nebraska at
Omaha, NE-68182
slancaster@mail.unomaha.edu
Telephone No: NA

Mansour Zand,
College of Information Science and Technology, University of Nebraska at
Omaha, NE-68182
mzand@mail.unomaha.edu
Telephone No: NA

Cobra Rahmani,
College of Information Science and Technology, University of Nebraska at
Omaha, NE-68182
crahmani@mail.unomaha.edu
Telephone No: 402-348-9190

Specifying Non-functional
Requirements for Real-Time Systems

Satish Srinivasan Scott Lancaster Mansour Zand Cobra Rahmani

College of Information Science and Technology, University of Nebraska at Omaha, NE-68182
smsrinivasan@mail.unomaha.edu
slancaster@mail.unomha.edu
mzand@mail.unomaha.edu
crahmani@mail.unomaha.edu


Abstract

Software or System Requirements often change during
their operational lifetime [4]. These changes take place
due to misconceived requirements perceived during the
requirement and design stages. These changes are
mostly evident during the run time of the system and so
they are known as emergent faults. These emergent
faults are unforeseen by the requirement engineers and
so there is no built-in fault tolerance solution for the
components in this system. In this paper we consider a
real-time multi-network system of Alegent Health,
where their application servers are used for critical
Electronic Medical Record (EMR) application. These
application servers frequently blow up due to memory
leakages. Due to memory leakage problem in the
application servers the performance of the system drops
down resulting in kicking off the users (doctor and
nurses) of the system, elevating concerns on patient
safety and also causing loss of revenue that worth tens
of thousands of dollars per hour. We attribute this
problem to be a misconceived non-functional
requirement and as an emergent runtime fault. We
propose a health monitoring system which will keep
track of the health conditions of the servers with the
objective of increasing overall system throughput,
decreasing system downtime, and minimizing loss of
data. We have proposed the use of the concept of
Duration Calculus to specify the non-functional
requirements of the system in terms of continuous state
variables and discrete state variables. After expressing
the non-functional requirements using the Duration
Calculus the architecture of the system can be verified
to see if it accounts for supporting the non-functional
requirements.

1. Introduction

Software Systems requirements engineering (RE)
is the process of identifying the concerns of the
stakeholders and documenting them in such a way that
it is amiable to analysis, communication, and
subsequent implementation [2]. The requirement
engineering process involves various phases like
gathering requirements, proposing architectural designs,
identifying the sub systems and developing them
individually, integrating the sub systems and validating
the system for its correctness [5]. The requirements of
the system can be classified as functional and non-
functional. The functional requirements are concerned
with the functionality of the system and the non-
functional requirements are system properties that
emerge from the combination of the system sub-parts.
According to Malan and Bredemeyer [7] the emergent
properties are matter of accidents and not design. If the
non-functional attributes are not captured properly in
advance then they could lead to system malfunction or
crash in the run time. In this paper we have considered
the memory leakage problem in the application servers
of the Alegent Health system. We believe that this
problem is due to misconceived non-functional
requirements (specifically emergent) which the system
engineers failed to catch in the requirement stage and
failed to verify in the design stage. This is a serious
problem as memory leakages leads to performance
degradation which indeed leads not only to loss of
revenue but also threatens patient safety.

We have tried to use the concept of Duration Calculus
[1, 6] for capturing the requirements of the Alegent
Health System. It is our belief that the Duration
Calculus can help in specifying the non-functional
requirements of the real-time system in terms of
continuous and discrete state variables and also help to
verify the architecture of the system. The next section
we give a short literature survey of previous research
work accomplished in this area.

2. Literature Survey

The Non-functional requirements are requirements
which are not concerned with the functionality of the
systems but are concerned with the external constraints
that the product must meet for example, safety,