Home > Articles > Software Development & Management > UML

  • Print
  • + Share This

The Lost Opportunity

Unfortunately, the Unified Modeling Language has failed in one of its main objectives. In fact, I would argue that it fails in the very area that should be its greatest promise, that of notation.

Graphical Notations: Why the Big Deal?

A design notation is intended as a means of communication. It is a lingua franca between engineers, ensuring unambiguous transfer of design ideas. Graphical notations are ideal for this in a number of ways:

  • Graphical notations transcend language boundaries. If an English designer draws a circuit diagram, a non–English-speaking electronics engineer can read that diagram and understand it.

  • Graphical notations scale. You can cram an awful lot of elements into a small space using well-designed graphical notations. For example, it's not uncommon to find electronic designs with 50 or more components in a diagram on an A4-sized piece of paper. One key reason for this is that "a picture paints a thousand words"—you can put an awful lot of semantic meaning into a well-designed icon. To express the same amount of information in words takes up much more space.

  • Graphical notations aid the identification of patterns. The eye/brain combination is very good at identifying visual patterns. Even in a complex diagram, the eye can recognize familiar graphical combinations.

Why UML Is Not a Graphical Notation

But UML is a graphical notation, I hear you cry! It's true that UML has many graphical elements, but I would argue that in some key areas it falls short:

  • Reliance on textual annotations—Many adornments rely on textual descriptions—for example, the include/extend on Use case diagrams or the {ordered} constraint on an association. There is no reason why graphical icons could not have been used for these. It's not just a case of not being able to read the words because of language differences—although that's an extra potential hazard. It is about the ability to scan and comprehend quickly what the diagram is trying to communicate.

  • Reliance on stereotypes—This reliance on text really starts to strike home when we consider the different types of classes that all use the same icon. Compare transistors in electronic engineering—there are at least 20 different, although similar, icons for a transistor, reflecting the different characteristics. Just a few of these are shown in Figure 1.

  • Figure 1

    Some icons for a transistor

    Why not do something similar for the different types of classes—for example, why not distinguish graphically between:

Meta classes

Abstract classes

Factory classes

Class utilities

Mix-ins

  • Nonstandard graphical icons via stereotypes—Ironically, one of the features of UML often held to be a strength is, in fact, a potential weakness: the ability to use stereotypes to change the icon representing an entity. This is most usually (and most sensibly) applied to physical deployment diagrams, where the default "node" icon is replaced by a clip art representation of the node—a Cisco router, a Sun server, and so on. This makes some sense. However, taking this further, there is nothing to stop a designer supplying his or her own icons for things such as classes, states, and use cases. This would render the notation completely unreadable to anyone unfamiliar with the changes, defeating the purpose of a standard notation. (The reason for allowing these changes is to permit extension of the notation to cover new requirements, a laudable but flawed goal.)

  • Overloading of symbols within a single diagram type—Components are probably the best (or should that be worst?) example of this. In a single diagram, a component symbol can represent a header file, an implementation file, a library, a folder containing multiple libraries, and so on. In another diagram context, the same symbol can represent a COM object (with interface adornments) or a logical subsystem or a class category (although many of these are better represented by packages rather than components, but the local confusion remains).

    Nodes in a deployment diagram suffer from the same fate. Everything from a mainframe to a PC to a router has the single square box node icon. Here stereotypes are recommended to differentiate, but once again we must rely on reading text to understand exactly what we are looking at. The alternative involves defining our own set of icons, which others may or may not understand. Worse still, they may think that they understand them but in fact make the wrong assumptions, which is exactly what a formal design notation is supposed to prevent!

What's Missing?

The deficiencies described are not the only areas where the UML is weak. UML is one of the few software design notations to even consider the physical aspects of the design process, so it might seem unfair to criticize this aspect, yet it is another case of being so close and yet not quite hitting the target. Two notable gaps exist in the design notation for describing the physical aspects of a system, as discussed next.

Process Diagrams

Grady Booch, in his original Object-Oriented Design book, illustrated the different aspects of design with a box cut into four quadrants. These quadrants represent logical and physical design, each of which had static and dynamic elements. While UML provides notational elements for static and dynamic aspects of the logical design, and some support for static physical design, the notation is almost completely lacking in any form of representation for dynamic physical design. In particular, the most dynamic of physical elements, the process, is missing entirely from the notation.

It possible to work around this in various ways, but nonetheless, it is a significant lapse. How does one describe interactions with the operating system services or daemons? What about replication of processes as an element of load balancing? Indeed, what about interprocess messaging both between nodes and within a single node? It is possible to represent these things using objects in an interaction diagram, but these rightly belong to the logical domain and indeed are often not even recognizable objects within the design proper. Finally, there are different types of processes to be represented, such as daemons, scheduled batch jobs, one-shot utilities, and so on. Even using objects to represent processes does not really address these kinds of environmental differences because the same executable could be run as either a batch job or a one-shot process or both, all within the same system.

Network Variations

Most software engineers represent networks as lines connecting two nodes or as a fluffy cloud. In the real world, especially in the sphere of systems integration, networks come in many forms with distinct characteristics:

  • Circuit-switched

  • Packet-switched

  • Virtual circuits

  • Analog

  • Digital

These characteristics make a big difference in the way that a large system operates and is constructed. Indeed, the very fact that multiple network types exist within a system and that these networks are not natively compatible is an issue worth highlighting in a design. It would be nice if both point-to-point network links and whole network "clouds" had distinct representations in UML showing the nature of the link. Whether an ethernet LAN is using a hub or a switch is likely to make a significant difference to how the system will perform under heavy load—probably a much bigger difference than how the code is written! At present, we have only a single node icon and some lines to represent all aspects of the hardware and network deployment.

  • + 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