John C. Kelly ( 434)
Welcome to the NASA Software Engineering Handbook (SWEHB). This wiki based handbook provides users and practitioners with guidance material for implementing the requirements of NPR 7150.2, NASA Software Engineering Requirements. Use of this SWEHB is intended to provide "best in class" guidance for the implementation of safe and reliable software in support of NASA projects. This SWEHB is a key component of the NASA Software Working Group's (SWG) implementation of an Agency wide plan to work toward continuous, sustained software engineering process and product improvements.
The SWG designed this handbook for the community that is involved in the acquisition, management, development, assurance, maintenance, and operations of NASA software. Readers can use it to sharpen their skills in specific areas or suggest valuable guidance for others in the NASA software community. Novice and experienced software team members can use the handbook as an easily accessible reference or manual which captures the broad knowledge base of numerous experts who have extensive experience in all aspects of NASA's software systems.
In this SWEHB you will see information for determining the scope and applicability of the individual requirements from NPR 7150.2. You will also see rationale, implementation guidance, tools used in the development of NASA software, pointers to key lessons learned, and select references for further information.
We have adopted the 'wiki' approach for this version of the handbook to encourage you to submit candidate improvements to the information in this handbook. Your comments, suggestions for improvement, offerings of additional candidate material for the handbook, and identification of errors are solicited to make this a living and ongoing source of useful information. You can use the 'Comments' box on almost any page of the wiki to submit your inputs and responses. The SWG's SWEHB team will review and disposition your comments to enhance the wealth of useful material which is now at the fingertips of NASA's software community.
We hope you find the information provided by many contributing experts, distilled into useful chunks by the SWEHB team, and jointly reviewed by NASA's SWG and MSSC ** members helpful in your day to day quest for engineering excellence.
* Chartered by the NASA Engineering Management Board and funded by the NASA Headquarters Office of Chief Engineer
** NASA Mission Software Steering Committee
(Contact the SWEHB site admin for resolution of technical difficulties.)
The NASA Software Engineering Handbook (SWEHB) originated from multiple requests for additional guidance, rationale, resources, references and lessons learned for acquiring, managing, developing, assuring and maintaining NASA software systems. The design of the electronic (
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- to publish material in a timely fashion
- to provide needed information in concise screen-friendly chunks
- to simplify updates to the handbook
- to make it easily searchable
- to engage the NASA software community by providing an easy-to-use vehicle for
- providing feedback
- sharing examples of best practices
- contributing lessons learned developed on their own projects
The SWEHB is accessible on the NASA Engineering Network 258. The Agency's software community will find they have complete and speedy access to all written content and reference links in the handbook through the NEN. An important set of links are also provided for relevant processes, templates, and tools in the NASA Process Asset Library (PAL).
The SWEHB wiki can be used in a similar manner to the use of hardcopy guidebooks, but it offers significant advantages for the reader. Once a general familiarity with the resource is obtained (typically a quick scan and flip through the Handbook structure, including the Chapter organization and the Reference/Appendix material), the user will be able to directly access concise information relevant to their interest or need.
Users are encouraged to provide general feedback on the SWEHB by using the 'Comments' box found on the wiki pages. Suggestions for improvements, identification of errors, and proposed additions to the SWEHB are all welcome. The SWEHB Development Team will review and disposition comments received. Additions, if approved for posting by the SWEHB editor, will be added via incremental updates.
The SWEHB is organized in a series of cross-linked Books (A through E). The basic information within these Books is presented in the form of essays that provide guidance on the implementation of each software engineering requirement (SWE). The SWEHB has other essays, called 'Topics', which are more expansive on particular ideas and contain additional instructions for developing and acquiring software.
The SWEHB provides guidance associated with each SWE-xxx requirement. Software developers: Take note - the information provided in these modules are only general approaches for Agency use. Users are expected to consult NASA Center resources for local procedures and guidance, when available.
Overview of each Book within the SWEHB:
- Book A contains the Introduction.
- Book B contains the developed guidance for each SWE. (Note that the SWE descriptions are organized in six Chapters within Book B that mirror the organization of NPR 7150.2). The SWE are presented in nominal ascending numerical order, with some higher numbered SWE intermixed. These latter SWE represent the changes made between the NPR 7150.2 and the NPR 7150.2A revisions. The SWEHB was written so each SWE guidance section provides stand alone explanations and interpretive information about the requirement. To enhance the usefulness of each module, the guidance include hyperlinks for easy reference to related SWEs and Topics.
- Book C contains special Topic discussions that are broader than any single SWE. Many of the special Topics take the form of 'how to' and instructional material for users seeking to improve their knowledge and practices in software engineering. It is expected that the special Topics will help the user go beyond the minimum descriptions presented in each SWE. Many Topic numbers are reserved at this time for future use.
- Book D lists the current tags (labels) that are used throughout the handbook. To further assist the user in finding needed and useful information, a 'tag" system has been developed using the SMARTS Tagging approach to indicate relationships between or among individual ideas contained within multiple SWEs. The tagging search feature in Book D allows both individual and multiple tag searching. Tag searches provide an additional way for users to browse and discover content within the handbook. The terms 'tag' and 'label' are used interchangeably in the handbook.
- Book E contains appendix and miscellaneous types of information that help the user get the most out of the SWEHB. These entries include listings of and references to software development tools that are used around the Agency, the full set of NPR 7150.2 requirements (it includes the complete text of the NPR 7150.2 requirements with links to each section in the handbook), and lists of terms used in the SWEHB.
Explanation of the SEARCH Box in the splash banner above: This utility allows the SWEHB user to interrogate the handbook contents for particular items of interest.
Tag searches are performed using the search tool in Book D.
In the SWEHB a typical SWE essay has six sections;
- THE REQUIREMENT: This section is a restatement of the NPR 7150.2 requirement wording, including any Notes from either the requirement paragraph itself, or any applicable note from Appendix D. This section also gives a tabular representation of the applicability to each software class.
The text in this section can only be altered via an approved change request and NODIS update of NPR 7150.2.
- RATIONALE: This section provides useful information regarding the purpose of the requirement. Occasionally, historical information and or references are included to further support the rationale statement.
- GUIDANCE: This section provides information helpful for interpreting the requirement, its scope, its relationship to other SWE, associated best practices, and references to supporting materials (standards, guides, published technical papers, the NASA Engineering Network 258 and the NASA Process Asset Library (PAL) 266 materials).
- SMALL PROJECTS: This section suggests implementation aids to small projects to help satisfy the SWE while accommodating the typically limited resources of time, funds, and personnel. The definition of 'small project' needs to be determined by the user.
This determination does not relieve a project from satisfying the requirements in the NPR.
- RESOURCES: This section provides a listing of referenced and footnoted texts, documents found within NASA repositories and / or out on the web, and other useful documents (e.g., checklists and/or templates). It is instructive to note that the handbook authors also included in the Resources sections listings of what might be best described as 'additional reading', i.e., useful items not specifically cited or linked to in the GUIDANCE section, but thought by the authors to contain educational or expanded discussions of the ideas covered in the SWE write-up.
Also within this section is usually a separate table listing of tools, items that will help the user satisfy the requirement (e.g., developer tools). The handbook wiki links SWEs and tools through the use of a master Tools table. The Tools table provides web sites for accessing the tool. It also lists Center(s) that currently use the tool in case the reader wants to seek out the 'experiences' of a current user of the tool. Readers are invited to submit their tools for candidate inclusion in the Tools table for the benefit of others around the Agency.
- LESSONS LEARNED (LL): This section contains references to the experiences of others involved in NASA software development activities as well as other industry and government development efforts. The majority are catalogued in the Public Lessons Learned library at the Office of the Chief Engineer (OCE). Some are derived from specialized project or Center collections as well as from reputable industry and government groups. Occasionally a lesson has only indirect applicability to the requirement. It is presented as a related lesson that can be applied to help understand the content of the SWEHB.
Remember that the NPR 7150.2 is a requirements document. It uses 'shall' exclusively to indicate requirements. Applicability of a NPR 7150.2 requirement is determined by NASA Software Classification and the matrix in Appendix D (of the NPR). The SWEHB is not a requirements document, only an informational document. NO new requirements are added by the SWEHB. The authors strove to exclude the use of 'shall' and 'should' in any paragraph that might be interpreted as a requirement or even an augmentation to a requirement.
The NPR 7150.2 made extensive use of the NPR's Notes sections to help with the interpretation of the SWE. This handbook is intended to collaborate with and to augment the NPR's Notes.
The Requirements Mapping Matrix (RMM) (Appendix D, NPR 7150.2) provides a list of the applicability of each requirement by the Class of software being developed. Associated with many of the entries in the RMM are one or more notes that modify the applicability of the requirement for a particular Class. Since the SWEHB makes explicit mention of these modifiers in section 1 of the SWE essay, an additional explanation for each note is included here:
- The "X" notation signifies that the full requirement (assuming no 'exceptions') is applicable to the software. Note that requirements labeled with an "X" can still be tailored with the appropriate approvals, or otherwise affected by approved deviations and or waivers.
- The "SO" (i.e., Safety Only) designation signifies that the requirement for the classification of software needs only to satisfy the safety aspects of the requirement. This may require the use of checklists (e.g., use of the 'litmus test') in NASA STD 8739.8 Software Assurance Standard and NASA STD 8719.13 Software Safety Standard to determine specifically what parts of the project, its software, and therefore the requirement, are applicable to ensure the development of safe software.
- The "P (Center)" designation, while amply described in [SWE-140], is used separately or in combination with the "SO" modifier. The "P (Center)" modifier is only applicable to the items of the requirement that do not incur a 'safety-critical' designation. The interpretation is consciously left to the individual Center Technical Authorities since they and their individual projects are unique, and this tends to make one universal applicable statement too inexact.
Some general comments:
- Note that the SWE titles in the SWEHB may not always agree with those in the NPR. The SWEHB Development Team expanded the titles for some of the SWE to help distinguish between other similarly sounding SWE names (e.g., 'bidirectional traceability').
- The SWEHB uses a
- Much of the referenced material listed in the Resources section is located on the NASA Headquarters NODIS site (e.g., NPR's, NPD's), in the Agency PAL (Process Asset Library; e.g., materials from the OCE, Public Lessons learned), or in the NASA Technical Standards repository (START); e.g., NASA standards, IEEE standards, etc.).
- Extensive citations are also made to external sites (e.g., Hill AFB at STSC, Software Engineering Institute-SEI), and to general web-hosted sites. While attempts were made to cite publically available (i.e., 'free') references, there may be an occasional reference that suggests the reader 'buy' a copy. If you come across one of these, try to access it through the NASA START (technical standards) site. A simple and quick registration is required. This NASA site provides prepaid access to many external repositories through an Agency wide agreement with the site.
- (Caveat: since the web is a dynamic place, some references in the Resources section of the SWE may be discontinued online or moved to another host by their owners).
Each page of the SWEHB has a 'Comments' box to allow feedback and proposed inputs, revisions, and updates to the Handbook. The SWEHB Development Team requests comments on errors, inputs on real or perceived conflicts among the essays within the SWEHB and suggestions for additional material such as best-in-class examples, templates, tools or lessons learned entries.