Home > Articles > Software Development & Management

An Overview of Strategies for Real-Time System Specification

  • Print
  • + Share This
The authors of Strategies for Real-Time System Specification introduce their book, which offers an indispensable guide for creating a systematic, formal methodology for large, real-time, software-based systems.

Read Strategies for Real-Time System Specification and more than 24,000 other books and videos on Safari Books Online. Start a free trial today.



This chapter is from the book

For more than a decade, there has been growing dissatisfaction with conventional strategies for systems development, and an increasing number of proposals for replacing them with new, more formal approaches. The problem is that conventional development methods cannot cope with the size and complexity of the systems we are now able to implement. These system characteristics are possible because of the ever-increasing capacity and capability of computer hardware. Systems having up to a million lines of high-order source code are already commonplace, and others are on the horizon that will require ten or more times that amount.

The inadequacies of the development methods were first apparent in large business and commercial systems, but as digital technology came into use in real-time embedded systems, they too became subject to the same problems. We are past the stage of wondering whether formal development methods are really needed. The question is, Can we keep pace with the capabilities of the technology using the methods we already have? What further extensions and improvements can we make to them? Can we devise better and more comprehensive methods?

A problem with past system specification methods has been that they each tend to address only one aspect of the system, whereas systems actually have many aspects, all of which need to be addressed. The methods described in this book seek to overcome this problem by addressing a number of these aspects in an integrated manner. From the functional requirements point of view, they address the aspects of processing, control, and timing. From the physical requirements point of view, they address the architectural specification of the system, and most importantly, they take account of the hierarchical and iterative nature of systems and of systems development. Figure 1.1 illustrates how the whole universe may be thought of as a hierarchy of systems. Any individual system may itself be expressed as such a hierarchy, and the progression down through its levels involves defining the requirements for the level below, then making decisions on the architecture or design of that level to meet those requirements, then repeating this procedure for the next level down, and so on. This perspective makes clear the adage that one person’s requirements are another person’s design: a cause of considerable confusion in earlier development methods, but an integral part of the methods addressed here.

Figure 1.1

Figure 1.1. The universal hierarchy of systems.

Before we delve into the details of the methods, we will give a brief historical account of their development. This will help you understand the situations that create the need for such methods, and will give you some insight into what it might take to introduce them into your own organization.

1.1 The Birth of the Requirements Model

The requirements specification model described in this book evolved at a major avionics systems development company. This evolution started in late 1982, and culminated two years later in the successful Federal Aviation Administration certification of a complex real-time, embedded avionics system for a commercial airliner. The system is now in widespread use in the airline industry.

At the time, the development effort was the largest we had ever undertaken. Previously, we had been without formal procedures for integrating the efforts of our system and software developers: We had depended on their individual communications with each other, and on the abilities of a few overworked lead engineers, in order to keep the various subsystems consistent.

There comes a point at which this just won’t do, a point at which the interactions between the subsystems are at least as complex as the subsystems themselves. Faced with this dilemma, and with the very real threat of a major disaster if we did not improve our performance, we investigated the formal development methods that already existed. We found a fairly mature set of methods that had been developed in the 1970s for large mainframe business applications, and that had been successfully applied in that field.

Several of the existing requirements definition methods were capable of representing the information processing parts of our systems, but they could not handle the complex control structures that large real-time systems also typically include. Since these control structures can be represented using finite state machine theory, we decided that we needed to integrate an established requirements definition method with finite state machine theory in a unified structure, and to do it so as to retain the benefits of both.

The requirements definition method that seemed to have the most merit was DeMarco’s structured analysis [4], so we chose this as the starting point. One of the greatest merits of the DeMarco method is its attention to human readability and understandability through the use of graphics. In addition, it shares with most other requirements definition methods the attributes of information abstraction, built-in self-consistency checking, and the ability to be self-indexing.

Because the project was already underway, we needed a requirements definition method immediately. During just two weeks of brainstorming and trial and error, we found the approach we were looking for—a way to partition a large finite state machine into pieces corresponding to the pieces of a structured analysis—and the requirements model described in this book was born. One week later, a group of development engineers took the first class in the new method. That first teaching effort was not a polished presentation, but the substance was there. As we gained experience in its use, we made some further improvements in our emerging method, but, surprisingly, it has never needed any fundamental changes.

The existing and widely used structured design method [11,19] was applicable (with very little modification) to the design definition of our real-time systems.

Introducing the model

The approach we took to introduce our new methods was contrary to that advocated by methods experts, who advise that methods be introduced on a small, low-visibility project. We did not have (and have never had) such a project, and in fact introduced the method on the largest, most critical project we had ever undertaken. To offset the risks in this situation, we established a Methods Team—a group of six people whose sole role was to make the methods work. The team members prepared and taught classes, provided consultation, solved problems as they arose, made improvements to the methods, and investigated ways to automate them.

If critical projects are the only kind your shop, too, ever has to work on, and you are about to introduce revolutionary new development methods, we recommend this approach of dedicating a team to support them.

It would be misleading to suggest that the requirements and design definition methods alone were responsible for the success of the project. We made a number of other changes at the same time: For example, a large scientific computer was dedicated to the project; each system and software engineer was provided with an interactive terminal; an efficient, modular working environment was installed; we scaled the project using the Putnam model [15]; and we used a more detailed and comprehensive progress tracking procedure than we had ever used before. The relative contributions of the individual factors are hard to judge, but their combined effect was greatly improved productivity.

One of the earliest decisions made with regard to the requirements model was to make it freely available to anyone wishing to use it, rather than to copyright it, or treat it as proprietary information. Our rationale was first, that our business is avionics, not development methods; second, that it would be to our advantage to have the rest of the industry follow our lead; and further, that it would be particularly advantageous to have automated tool developers embed our method in their tools. As a result of this early decision (and because of the success of the requirements model in its first application), the method has become widespread in the industry. Many diverse companies are using it, and there are currently at least six automated CASE tool developers [21] supporting it (some more completely than others—we neither endorse nor recommend against these or any other CASE tools; you must evaluate them relative to your own needs and environment). In addition, there are seminars [20] available giving instruction in the use of both the requirements and the architecture models. This popularity has given rise to constant demands for more available information on the method, and these demands provided our principal motivation for writing this book.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020