Home > Articles > Programming

  • Print
  • + Share This
This chapter is from the book

How Do You Understand Systems?

Understanding a large and complex system is difficult. You can only understand it by controlling the amount of information you take in at a time.

Let’s leave the cavemen’s system for a moment and find an example in the twentieth century to illustrate. Suppose that you, a systems analyst, need to understand an automobile. Assume that you have only the most rudimentary knowledge of how a car works and that an expert is available to explain the car. Although cars are made of hundreds of individual components, initially you do not have to know anything about any of them.

In the beginning, the most useful information your expert can give you is an explanation of how the major components of the car interact with the others to produce the desired result. This means, of course, that the major components are fairly large things such as the engine, transmission, suspension, and body. For the moment, you must accept that each component works as the expert says it works, and not be concerned with how it accomplishes its task.

Once you understand the complete system in terms of the interactions between the major components-the engine powers the wheels, the body rides on the suspension, and so on-then you can begin to investigate how each of the components at this level works. Again, you must accept an explanation of the interaction between subcomponents, and believe for the moment that the subcomponents all work. Ensure that you understand this level of detail before investigating the subcomponents.

Each of the subcomponents is in turn broken into its subcomponents, and this partitioning continues until you arrive at a level of detail such that any component is so understandable you don’t have any more questions. Its function is obvious, or it can be described without benefit of any further partitioning.

How far do you go with the partitioning of a system? With the automobile example, you can continue dividing and subdividing until the components are single pieces of metal, or until you get to the molecules of the alloy, or perhaps until you reach the fundamental particles that make up the atoms. The answer is that it depends on your purpose when you study a system.

In systems analysis, we use the convention of head-sized pieces: pieces of the system that comfortably fit inside an analyst’s head and are readily understood. In the automobile example, the engine of the car is larger than head-sized, whereas the carburetor is just about right. For information systems, head-sized pieces are those that can be satisfactorily specified in a page or less of text description. These descriptions are called mini specifications, and they are the topic of Chapter 2.12 Mini Specifications.

The alternative to a leveled, successively detailed approach to understanding systems is too awful to contemplate. Suppose that in trying to understand the car, you started at the nuts-and-bolts level or the sub-sub-subcomponent level. How many sub-sub-subcomponents are there? Too many to let you easily understand how a car works. By starting at this level, you’d be swamped with details to the point that you’d probably never understand the system. The advantage of a leveled approach is that you move into the details as you choose. When you are controlling the amount of detail, you are far more likely to succeed with your goal of understanding the entire system.

Now look back at the cavemen’s hunting system. Hunting was just part of their lives. If you were studying anthropology and wanted to understand the ways of the cave people, you’d not likely first study their recipe for the barbeque sauce they used on the woolly mammoth. Instead, you’d first look at a higher level to study all of their activities: hunting, gathering, painting the cave walls, clubbing other tribes, and so on. Then you would study each activity that you identified. You would produce the hunting system diagram for study at this level, and then you might go on to look at even lower-level details, such as how they made their tools, how they mixed the paint for the cave walls, and so on. Eventually, by progressively descending into more and more details, you would capture all the activities as well as the links between them. This method is called a top-down approach.

Making Functional Pieces

The tactic of breaking large systems into progressively smaller components seems wise. However, you must ensure that you do produce useful components. There is little point in randomly chopping up systems in the way that Lizzie Borden partitioned her parents. When you divide a system, the resulting components must have some rational relationship to how the system works. In other words, each component must be a functional piece of the system.

How do you tell if you have functional components? First, a component is functional if it can be easily and informatively named, and if the name makes sense in the context of the system. Second, if you can honestly name a component using a verb and an object, it is a function. For instance, a name like SELECT AMBUSH LOCATIONS indicates that the component has a single function. It can be recognized by the user, and described by the analyst. A name such as PROCESSES BEGINNING WITH “M” does not pass the test and indicates that the partitioning didn’t produce functional processes.

We can also tell a lot about the functionality of a process by inspecting its interfaces—the data flows that enter and leave it. These flows should carry as little data as possible, and thereby make narrow interfaces.

Functional components need less data than do nonfunctional ones. Imagine the data flows for the two processes mentioned above. The data for SELECT AMBUSH LOCATIONS are reasonable (Figure 2.1.2). However, in any modern system, a process called PROCESSES BEGINNING WITH “M” would have an absurdly large number of data flows and, as a result, be meaningless to users. While functional components make narrow interfaces (alternatively, narrow interfaces make functional components), both are easier to get if you find the right places to divide the system.

Figure 2.1.2

Figure 2.1.2: Part of a model showing the data for SELECT AMBUSH LOCATIONS.

Cutting at the Natural Joints

Clearly, a woolly mammoth was too large to be cooked all at once, so the cave dwellers prepared it for cooking by cutting it into pieces. When they butchered the animal with their primitive tools, they cut along the soft natural joints, where it was easier to cut through than the hard bones. Similarly, many fruits, like oranges, provide natural seams for dissection.

The same is true in systems analysis. The natural joints in the system are along the narrowest interfaces, or where you find a narrow flow of data with two processes. If you try to divide the system by pulling apart functions, you’ll get messy interfaces. By partitioning where you find the data interface at its narrowest, you’ll deliver a model with functional components that are easy for the users to recognize.

  • + 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.


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.


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.


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.


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


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


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.


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.


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