The Software Cost Engineering (SCE) methodology developed over the last two decades at IBM Systems Integration Division (SID) in Houston is utilized to cost the NASA Space Station Data Management System (DMS). An ongoing project to capture this methodology, which is built on a foundation of experiences and lessons learned, has resulted in the development of an internal-use-only, PC-based prototype that integrates algorithmic tools with knowledge-based decision support assistants. This prototype Software Cost Engineering Automation Tool (SCEAT) is being employed to assist in the DMS costing exercises. At the same time, DMS costing serves as a forcing function and provides a platform for the continuing, iterative development, calibration, and validation and verification of SCEAT. The data that forms the cost engineering database is derived from more than 15 years of development of NASA Space Shuttle software, ranging from low criticality, low complexity support tools to highly complex and highly critical onboard software

Henson, Troy

Rone, Kyle

English

NASA Technical Reports Server

KNOWLEDGE-BASED ASSISTANCE IN COSTING THE SPACE STATION
DMS
N9 1 - 10 6 1"1
Troy Henson and Kyle Rone
m _
3700 Bay Area Blvd
Houston, TX 77058
ABSTRACT
The Software Cost Engineering (SCE) methodology developed over the last
two decades at IBM Systems Integration Division (SID) in Houston is uti-
lized to cost the NASA Space Station Data Management System (DMS). An
ongoing project to capture this methodology, which is built on a founda-
tion of experiences and "lessons learned", has resulted in the development
of an internal-use-only, PC-based prototype that integrates algorithmic
tools with knowledge-based decision support assistants. This prototype
SCEAT (Software Cost Engineering Automation Tool) is being employed to
assist in the DMS costing exercises. At the same time, DMS costing serves
as a forcing function and provides a platform for the continuing, itera-
tive development, calibration, and validation and verification of SCEAT.
The data that forms the cost engineering database is derived from more
than 15 years of development of NASA Space Shuttle software, ranging from
low criticality, low complexity support tools to highly complex and highly
critical onboard software.
INTRODUCTION
Software cost engineering (SCE) is the systematic approach to the esti-
mation, measurement, and control of software costs on a project. This
discipline provides the vital link between the concepts of economic
analysis and the methodology of software engineering. The tasks involved
in software cost engineering are complex, and individuals with the know-
ledge and skill required are scarce (I). The accuracy and consistency
of the SCE results are often questionable (2). There is a definite need
for tools to enable SCE by managers and planners who are not experts and
to improve the results (3).
PROBLEM DESCRIPTION
Software costing is required for the Space Station Data Management System,
as in other projects, in many situations. Often the costing is needed
within a limited time frame for a proposal, to build a business case, or
to evaluate a project that is in trouble or potentially may have a problem
meeting cost and schedule constraints if not adjusted. Quantitative es-
T. Henson
IBM
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https://ntrs.nasa.gov/search.jsp?R=19910001298 2020-03-19T20:27:26+00:00Z
timates are required; however, little solid information may be available.
A detailed analysis of the software requirements may take weeks if not
months. Also, there may be a geniuine concern about how well the software
requirements are defined and how stable are those requirements.
To further complicate the situation the estimation process itself carries
some inherent risks. Some of the factors that increase risk are software
size, complexity and criticality.
Software size, particularly in a system such as the Space Station DMS,
is an important factor that can ultimately affect the accuracy of the cost
estimate. As the project size increases the interdependency among various
elements of the software increases. Problem decomposition, an important
step in the costing process, becomes more difficult.
Complexity, i.e., the relative difficulty of the software application,
is an important factor affecting development costs. Some types of soft-
ware are inherently more difficult to develop than others, e.g., devel-
opment of an operating system compared to the development of utility
software. The type of software function, such as real-time, input/output,
batch, or computational, and the level of difficulty of the requirements
also significantly influence software complexity.
The criticality of the software directly affects the cost of validation
and verification as well as indirect costs. Software for certain medical
diagnosis or treatment systems, for air traffic control, or for the Space
Shuttle Flight Control System must not fail or human lifes will be lost.
In contrast, an inventory control system should not fail, but the impact
of the failure would not result in the loss of human life.
Viable software costing depends on a quantitative historical database.
If no historical data exists, the cost estimation rests on a very shaky
foundation. For Space Station DMS, as for other IBM SID Houston projects,
the cost engineering database is based on more than 15 years of develop-
ment of NASA Space Shuttle software, ranging from low criticality, low
complexity support tools to highly complex and highly critical onboard
software (4), (5).
KNOWLEDGE-BASED SCE AUTOMATION -- SCEAT DEVELOPMENT
Currently at IBM SID in Houston, software cost engineering tasks are
performed by a domain expert using his/her experience and data compiled
from previous efforts. For a software costing exercise, the domain expert
may use stored data and algorithmic/model-based, costing programs; but a
significant part of the process is based on non-automated expertise.
Software costing expertise is needed in many situations, and the costing
is often needed within a limited time frame. Yet, individuals with the
knowledge and skill to conduct a software costing exercise are scarce.
The knowledge-based decision support assistants in SCEAT identify and
preserve the domain experts' knowledge, assist managers and planners who
are not costing experts, and improve the accuracy and consistency of the
cost estimation results.
T. Henson
IBM
2 of 19
As part of the knowledge acquisition process, the first draft of a soft-
ware cost engineering workbook has been written and utilized as high-level
requirements for SCEAT. The overall SCE process was analyzed from a
modular/structural/dependencies viewpoint. Included is the relationship
of SCE methodologies to other parts of software/systems engineering
process control, at one end of the spectrum, and the decomposition of SCE
into component tasks and the identification of the SCE foundation or
central core, at the other end of the spectrum (See Figures i and 2).
Then a concise approach to software cost estimation, which covers the
total costs -- direct and indirect -- over the complete life cycle, using
existing methodologies and tools and quantification of the primary domain
expert's knowledge (6), (7) was defined. The experience-based tasks in
the SCE process were identified, and the functional design of SCEAT in-
cludes expert systems to assist in those tasks. The core development cost
estimation methodology was defined in the SCE workbook in more detail and
implemented in the initial SCEAT prototype, which includes prototypes of
expert systems for assistance in determining software criticality and
software complexity.
The SCEAT prototype integrates, under Professional Work Manager (PWM) and
EZ-VU on a PC, algorithmic SCE tools with expert systems for decision
support assistance. SCEAT integrates the decision support assistant ex-
pert systems for software criticality and complexity determination and
"stubs" for four additional planned expert systems with nine algorithmic
tools including the Matrix Method tool implemented in Lotus 1-2-3. The
user interface is via panels offering cook book steps to proceed through
the SCE task, selectable information and tools, help screens, and pop-up
screens.
COSTING THE SPACE STATION DMS UTILIZING SCEAT
The SCEAT prototype has been utilized to assist in the costing of the
Space Station Data Management System (DMS), a complex software system
involving a distributed environment with multiple languages and applica-
tions (8), (9). The DMS for Space Station is also affected by the re-
quirements for long lifetime, permanent operations, remote integration,
and phased technology insertion of productivity tools, applications, ex-
pert systems, etc. Major cost drivers include the large size and diver-
sity of the software, complexity, development support environment,
off-the-shelf and reusable software, and criticality, which varies from
one module to another. An example of the type of results -- at the end
of the intermediate step of development cost estimation -- obtained with
SCEAT for the DMS costing is included in the presentation.
SUMMARY/CONCLUS IONS
The software cost engineering methodology employed by the domain experts
at IBM SID Houston has been captured and integrated into a prototype tool
SCEAT (Software Cost Engineering Automation Tool). This PC-based tool
integrates algorithmic tools with expert systems which serve as decision
support assistants.
T. Henson
IBM
3 of 19
SCEAT has been employed to assist in the costing of the Space Station DMS
(Data Management System). It is providing a standardized approach for
the DMS costing, which involves several individuals. It has made the
costing process more efficient and has relieved the demands on the prin-
cipal domain expert's time, allowing him to move forward into other areas
of software/systems engineering process control improvement. The auto-
mation and captured methodology domain knowledge has established the
foundation and mechanism enabling the continuing calibration and im-
provement in accuracy and consistency for Space Station DMS costing.
Plans for the future include developing additional knowledge-based deci-
sion support assistants and a tutorial to accompany the next version of
SCEAT. The approach is also being expanded to other areas of
software/systems engineering process control, starting with quality es-
timation, scheduling and management, and eventually extending to manage-
ment of_performance, product, resources, risk, planning, schedule. (See
Figure 1). This is a continuation of the effort to accomplish the long
range objective which is to automate, including the development and
utilization of knowledge-based systems to serve as decision support as-
sistants, software and systems engineering process control. Results will
continue to be applied to assist in the costing and management of the
Space Station Data Management System (DMS).
REFERENCES
i. DeMarco, T., Controlling Software Projects, Yourdon, New York, 1982.
2. Kemerer, C. F., "An Empirical Validation of Software Cost Estimation
Models," COMMUNICATIONS of the ACM, Vol. 30, No. 5, May 1987, pp
416-429.
3. Boehm, B. W., "Improving Software Productivity," COMPUTER, Vol. 20,
No. 9, September 1987, pp 43-57.
4. Madden, W. A. and K. Y. Rone, "Design, Development, Integration:
Space Shuttle Primary Flight Software System," COMMUNICATIONS of the
ACM, Vol. 27, No. 9, September 1984, pp 914-925.
5. Spector, A. and D. Gifford, "The Space Shuttle Primary Computer Sys-
tem," COMMUNICATIONS of the ACM, Vol. 27, No. 9, pp 874-901.
6. Rone, K. Y., "A Cost Engineering Overview," class notes and handouts,
March 29-30, 1988, IBM SID, Houston, Texas.
7. Rone, K. Y., "Software Engineering Process Control," copy of presen-
tation, IBM FSD, Houston, Texas, 59 pages.
8. Chevers, E., "Avionic Systems Test Beds for Space Station," Plenary
Presentation at the JAIPCC (Joint Applications in Instrumentation,
Process, and Computer Control), sponsored by the IEEE, ISA, and the
University of Houston Clear Lake (UH-CL), March 12, 1987, UH-CL,
Houston, Texas.
9. Heer, E. and H. Lum, "Raising the AIQ of the Space Station," Aerospace
America, January 1987, pp 16-17.
T. Henson
IBM
4 of 19
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Knowledge-based assistance in costing the space station DMS

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