Engineering topics
Publications and source records attributed to Legrand, Sue.
Information on the Ada programming language is given. Topics covered include computer graphics, uniformity issues, Ada maintenance, and real time extensions.
NASA is seeking an operating system interface definition (OSID) for the Space Station Program (SSP) in order to take advantage of the commercial off-the-shelf (COTS) products available today and the many that are expected in the future. NASA would also like to avoid the reliance on any one source for operating systems, information system, communication system, or instruction set architecture. The use of the Portable Operating System Interface for Computer Environments (POSIX) is examined as a possible solution to this problem. Since Ada is already the language of choice for SSP, the question of an Ada/POSIX binding is addressed. The intent of the binding is to provide access to the POSIX standard operation system (OS) interface and environment, by which application portability of Ada applications will be supported at the source code level. A guiding principle of Ada/POSIX binding development is a clear conformance of the Ada interface with the functional definition of POSIX. The interface is intended to be used by both application developers and system implementors. The objective is to provide a standard that allows a strictly conforming application source program that can be compiled to execute on any conforming implementation. Special emphasis is placed on first providing those functions and facilities that are needed in a wide variety of commercial applications
The purpose of this research activity was to develop a list for NASA of major U.S. government information systems contacts who are able to cooperate with NASA on technical interchange. The list contains the names of appropriate managers involved in major information system projects, U.S. government office officials, and their hierarchy up to the highest officials whose major responsibilities include government information systems development.
The types of control that are important for real time task scheduling are discussed. Some closely related real time issues are mentioned and major committee and research activities in this area are delineated. Although there are some problems with Ada and its real time task scheduling, Ada presents fewer than any known alternative. Ada was designed for the domain of real time embedded systems, but Ada compilers may not contain a level of task scheduling support that is adequate for all real time applications. The question addressed is which implementations of Ada's task scheduling are adequate for effective real time systems for NASA applications.
The choice of Ada for software engineering for projects such as the Space Station has resulted in government and industrial groups considering training programs that help workers become familiar with both a software culture and the intricacies of a new computer language. The questions of how much time it takes to learn software engineering with Ada, how much an organization should invest in such training, and how the training should be structured are considered. Software engineering is an emerging, dynamic discipline. It is defined by the author as the establishment and application of sound engineering environments, tools, methods, models, principles, and concepts combined with appropriate standards, guidelines, and practices to support computing which is correct, modifiable, reliable and safe, efficient, and understandable throughout the life cycle of the application. Neither the training programs needed, nor the content of such programs, have been well established. This study addresses the requirements for training for NASA personnel and recommends an implementation plan. A curriculum and a means of delivery are recommended. It is further suggested that a knowledgeable programmer may be able to learn Ada in 5 days, but that it takes 6 to 9 months to evolve into a software engineer who uses the language correctly and effectively. The curriculum and implementation plan can be adapted for each NASA Center according to the needs dictated by each project.
The use of the Ada language does not guarantee that data objects will be in the same form or have the same value after they have been stored or transferred to another system. There are too many possible variables in such things as the formats used and other protocol conditions. Differences may occur at many different levels of support. These include program level, object level, application level, and system level. A standard language is only one aspect of making a complex system completely homogeneous. Many components must be standardized and the various standards must be integrated. The principal issues in providing for interaction between systems are of exchanging files and data objects between systems which may not be compatible in terms of their host computer, operating system or other factors. A typical resolution of the problem of invalidating data involves at least a common external form, for data objects and for representing the relationships and attributes of data collections. Some of the issues dealing with the transfer of data are listed and consideration is given on how these issues may be handled in the Ada language.
The Space Station contains safety critical computer software components in systems that can affect life and vital property. These components require a multilevel secure system that provides dynamic access control of the data and processes involved. A study is under way to define requirements for a security model providing access control through level B3 of the Orange Book. The model will be prototyped at NASA-Johnson Space Center.
NASA's software engineering and Ada skill base are assessed and information that may result in new models for software engineering, Ada training plans, and curricula are provided. A quantitative assessment which reflects the requirements for software engineering and Ada training across NASA is provided. A recommended implementation plan including a suggested curriculum with associated duration per course and suggested means of delivery is also provided. The distinction between education and training is made. Although it was directed to focus on NASA's need for the latter, the key relationships to software engineering education are also identified. A rationale and strategy for implementing a life cycle education and training program are detailed in support of improved software engineering practices and the transition to Ada.
The Common APSE Interface Set (CAIS) is a proposed MIL-STD intended to promote the portability of Ada Programming Support Environment (APSE) tools written in Ada. The standardized interfaces define a virtual operating system, from which portable tools derive their basic services, e.g., file management, input/output, communications, and process control. In the Ada world, such a virtual operating system is called a Kernel Ada Programming Support Environment (KAPSE). The CAIS is a standardized interface between KAPSEs and tools. The CAIS has been proposed as a starting point for standard interfaces to be used in the NASA Software Support Environment (SSE) for the Space Station Program. The status of the CAIS standardization effort and plans for further development are described.