TweetFollow Us on Twitter

Oct 01 Cover Story

Volume Number: 17 (2001)
Issue Number: 10
Column Tag: Software Engineering

Frameworks

by Paul E. Sevinc, Switzerland

Introduction

Reuse is a key objective of software engineering. In our January 2001 article [15], we discussed how reuse is achieved by the use of patterns. To recap, we saw that patterns promote analysis, architecture, or design reuse, but never implementation reuse. A framework supplies the mechanisms that enforce a policy for interaction between software entities with open implementations [2]. As we shall see, frameworks always promote analysis, design, and implementation reuse, but not always architecture reuse.

In this article, we briefly review libraries and toolkits as a point of comparison for frameworks. Then we discuss in more detail object-oriented frameworks. Finally, we touch on the issue of black-box vs. white-box reuse.

Libraries and Toolkits

Szyperski [17, p. 134] notes that "[e]arly programming languages attempted to provide all functions that would ever be used in multiple programs. An explosion of built-in functions was the result. [...] Since then, there has been a clear tendency to take specific functionality out of languages, in favor of abstractional and structural features." The specific functionality that was taken out, as well as additional functionality, was put in libraries. (As explained at the end of this section, toolkits are just special types of libraries.) The evolution of Pascal over Modula-2 to Oberon [11] is but one witness of this tendency.

The primary purpose of software libraries is to provide software engineers with reusable pieces of code (i.e., implementation). The most common kinds of libraries are procedure libraries (also called function libraries) and class libraries.

The Mac Toolbox/Carbon [1] is an example of a procedure/function library. It is designed and implemented in a procedural fashion to be used with a procedural programming language such as Pascal or C. Note that it not only defines procedures/functions, but also data structures (i.e., RECORDs and structs).

The C++ Standard Library [16] is an example of a class library. It is designed and implemented in an object-oriented fashion to be used with an object-oriented programming language, namely C++. Just like C++ is not a purely object-oriented programming language (as opposed to Java for instance), but a hybrid programming language, the C++ Standard Library is not a pure class library. Rather, it is a library of libraries, some of which are class libraries.

Toolkits are simply class libraries whose classes are related [5]. An example is the Java Abstract Window Toolkit (AWT), a library of classes for graphical user interfaces (GUIs) [6].

Libraries vs. Frameworks

First of all, let us dispel a common misconception: frameworks are not exclusive to the realm of object orientation. Oberon microsystems, for instance, have an amazing component framework in their product line [10]. And numerous frameworks have been realized in a procedural programming language such as C. However, we have to add that in the latter case, procedure variables/function pointers are typically used to mimic polymorphism. That said, we nevertheless confine ourselves to object-oriented frameworks, nowadays the most typical kind of frameworks, in the next section.

Whatever the paradigm used, the key difference between libraries and frameworks lies in whether the client is in charge or not:


Figure 1: Library vs. Framework [9].

In procedural programming, the client of a procedure library develops the main procedure and calls library procedures at her own discretion (see Figure 1 left). In a similar manner, when using a class library, the user-defined classes are in control and determine the overall architecture of the system.

The opposite is the case when development is based on frameworks; the framework decides when the user's methods are invoked. Thus, there is an inversion of control; the framework incorporates the control logic [5, 12] (see Figure 1 right). (The way this is realized in object-oriented frameworks is explained in the next section.) This is called the Hollywood principle: "Don't call us, we'll call you!" [9] or the Greyhound principle: "Leave the driving to us." [2].

Examples: The Java Platform Math Class and Model-View-Controller in Swing

The Java Math class [6] defines mathematical functions (e.g., sin) as well constants (e.g., e) and as a whole is obviously a function library. Client code that invokes one of Math's methods relinquishes control only for a split second and does not have to worry about any side effects.

The Model-View-Controller (MVC) pattern [5, 9] depicted in Figure 2 underlies Java's Swing GUI elements [6]. In the case of a text field, for instance, the model manages the actual text in memory, the view displays the text on screen, and the controller determines the text's editability.


Figure 2: Components of the MVC [9].

We are not restricted to using the text field as is. Any of its three constituent parts can be replaced independent of the others by a subclass (e.g., the default controller in order to accept numerical characters only). That and the fact that the methods our subclass overrides are—or in a good design at least should be—invoked only by non-client code make the text field a framework.

Object-Oriented Frameworks

An object-oriented framework is a customizable implementation of software. It consists of a set of cooperating classes and has hot spots [9] (also called plug points [4]), which make the customization possible (see Figure 3).


Figure 3: Framework [9].

Hot spots are abstract, or at least non-final, classes. Through factory, template and hook methods [5], the framework invokes the methods on the subclasses of the hot spots (see Figure 4). But it maintains overall control and makes sure that certain core tasks are fulfilled.


Figure 4: HotSpot [9].

Example: JUnit

JUnit is a framework for unit testing in Java [7]. Its original authors are Kent Beck and Erich Gamma, but it is maintained by an open community of software engineers. JUnit's four core types are partially depicted in Figure 5.

Clients of the framework subclass TestCase to add one or more methods that actually conduct tests. That is, TestCase is a hot spot. The three TestCase methods shown in italic are not really abstract: setUp and tearDown are empty hook methods invoked by the template method run before and after runTest, respectively. And runTest's default implementation invokes the client-added test method designated by the fName field using reflection.


Figure 5: JUnit Extract (adapted from [3]).

Let us discuss the use of the fName field a little bit more. As we already mentioned, a TestCase subclass can define more than one test method to test different aspects of a class or a set of classes. Typically, runTest invokes only one client-added test method (because setUp and tearDown should be invoked before and after every test method, but only by run in order to keep the design clean). Therefore, the TestCase subclass has to be further subclassed to override runTest for each test method. Alternatively, the TestCase subclass is not subclassed further. Instead, fName is defined to contain the name of different test methods for different instances. The latter approach is obviously simpler (albeit less type safe). (Using reflection in this way within an object-oriented framework allows for what could be considered "run-time parameterizable hot-spots".)

Beck and Gamma [3] treat the core design of the JUnit framework (using the language of design patterns) in more detail.

Application and Domain-Specific Frameworks

Frameworks can be domain-specific. FEMO, for instance, is a framework for multiobjective optimization with genetic algorithms [13]. Applications that make use of FEMO relinquish control during optimization runs, but FEMO does not impose any architecture on the application as a whole. Therefore, FEMO promotes analysis, design, and implementation reuse: analysis of the domain, and design and implementation of the classes.

An application framework is a standard program that takes care of window management, menu handling, opening & saving documents, etc., but that has to be extended by the programmer to give them content. Mössenböck [9] calls this programming by difference. Metrowerks' PowerPlant [8] is a typical application framework and as such defines the overall architecture of every PowerPlant-based application.

Black-Box vs. White-Box Reuse

A black-box framework hides its implementation from its clients whereas the implementation of a white-box framework is visible to—and possibly modifiable by—its clients. A glass-box framework is a white-box framework whose implementation is not modifiable. [18] (Note that, rather confusingly, frameworks are sometimes designated as white-box as soon as they emphasize implementation inheritance over object composition [17], whether the implementation is actually visible to the client or not.)

Black-box reuse is preferable over white-box reuse. With the former, when (part of) the framework is replaced by a new release whose interface and specification have not changed, client code should not break. With the latter, the implementation may have to be studied anew, since at least informally it was part of the contract.

Listing 1

method( Type parameter )
   throws IllegalArgumentException
{
   if ( parameter == null || !inRange( parameter ) ) {
      throw new IllegalArgumentException();
   }
   ...
}

For example, after studying its source code, some clients of the white-box method method in Listing 1 might rely on NullPointerExceptions (which are unchecked exceptions in Java and thus need not be declared in the exception specification) never being thrown. In a future version, method no longer checks for null references (see Listing 2), which—let us assume—it never advertised to do anywhere in its formal documentation in the first place. At compile time, all of the existing clients will compile just fine. At run time, however, some might now behave erroneously.

Listing 2

method( Type parameter )
   throws IllegalArgumentException
{
   if ( !inRange( parameter ) ) {
      throw new IllegalArgumentException();
   }
   ...
}

To Probe Further

Mössenböck's Objektorientierte Programmierung in Oberon-2 [9] is an excellent book on object orientation in general. The latest edition features a chapter on frameworks. Unfortunately, this edition has never been translated to English.

Gamma et al.'s Design Patterns [5] is first and foremost a book on, well, design patterns. Nevertheless, it also quickly introduces frameworks and discusses the important relationship between patterns and frameworks.

Szyperski's Component Software [17] is a seminal work on component orientation. It features a chapter discussing reuse in general, including a concise treatment of frameworks.

Acknowledgments

This article is partly based on a chapter in my M.S. thesis [14] that was proofread and commented on by Prof. Dr. Rachid Guerraoui, Dr. Jean-Philippe Martin-Flatin, Luc Girardin, and Dani Seelhofer.

I would like to thank the contributing reviewers for this article, Nate Little and Peter "Primetime" Taylor from Trilogy Software, Inc.

References

  • [1] Apple Computer, Inc. Carbon Developer Documentation. Home Page. Located at
    http://developer.apple.com/techpubs/macosx/Carbon/carbon.html.
  • [2] B. Appleton. "Patterns and Software: Essential Concepts and Terminology". Available at
    http://www.enteract.com/~bradapp/docs/.
  • [3] K. Beck and E. Gamma. "JUnit: A Cook's Tour". Java Report, Vol. 4, No. 5, May 1999.
  • [4] D.F. D'Souza and A.C. Wills. Objects, Components, and Frameworks with UML: The Catalysis Approach. Addison-Wesley, Reading (Massachusetts), 1999.
  • [5] E. Gamma, R. Helm, R. Johnson, and J. Vlissides. Design Patterns: Elements of Reusable Object-Oriented Software. Addison-Wesley, Reading (Massachusetts), 1995.
  • [6] C.S. Horstmann and G. Cornell. Core Java: Fundamentals. Sun Microsystems Press, Palo Alto, 5th edition 2001.
  • [7] JUnit.org. JUnit, Testing Resources for Extreme Programming. Home Page. Located at
    http://www.junit.org/.
  • [8] A. Montgomery. "First Steps". MacTech Magazine, Vol. 17, No. 4, April 2001.
  • [9] H. Mössenböck. Objektorientierte Programmierung in Oberon-2. Springer, Heidelberg, 3rd edition 1998.
  • [10] Oberon microsystems, Inc. BlackBox Component Builder. Home Page. Located at
    http://www.oberon.ch/prod/BlackBox/index.html.
  • [11] M. Reiser and N. Wirth. Programming in Oberon: Steps beyond Pascal and Modula. Addison-Wesley, Reading (Massachusetts), 1992.
  • [12] S.R. Schoch. Classical and Object-Oriented Software Engineering: With UML and Java. McGraw-Hill, Boston, 4th edition 1999.
  • [13] P.E. Sevinç. Ein C++-Framework für die Mehrzieloptimierung mit genetischen Algorithmen. Semester Thesis, Swiss Federal Institute of Technology Zurich, January 1999.
  • [14] P.E. Sevinç. Design Patterns for the Management of IP Networks. M.S. Thesis, Swiss Federal Institute of Technology Zurich, February 2000.
  • [15] P.E. Sevinç. "Patterns". MacTech Magazine, Vol. 17, No. 1, January 2001.
  • [16] B. Stroustrup. The C++ Programming Language. Addison-Wesley, Reading (Massachusetts), 3rd edition 1997.
  • [17] C. Szyperski. Component Software: Beyond Object-Oriented Programming. Addison-Wesley, Reading (Massachusetts), 1998.
  • [18] C. Szyperski. "Components and Objects Together". Software Development, Vol. 7, No. 5, May 1999. Available at
    http://www.sdmagazine.com/breakrm/features/s995f2.shtml.

Paul E. Sevinç is back in Europe after spending three fantastic months in Austin, Texas going through Trilogy University, the corporate boot camp of Trilogy Software, Inc. You can reach him at paul.sevinc@ubilab.org.

 
AAPL
$103.30
Apple Inc.
+0.80
MSFT
$45.09
Microsoft Corpora
-0.34
GOOG
$577.33
Google Inc.
+5.73

MacTech Search:
Community Search:

Software Updates via MacUpdate

TextSoap 7.4.0 - Flexible text editing u...
TextSoap is for people who work with text. TextSoap effortlessly cleans up text from endlessly different formats. Wash away unwanted characters, spaces, tabs. Fix paragraphs with hard returns at the... Read more
NetShade 6.0.2 - Browse privately using...
NetShade is an Internet security tool that conceals your IP address on the web. NetShade routes your Web connection through either a public anonymous proxy server, or one of NetShade's own dedicated... Read more
Mac DVDRipper Pro 5.0 - Copy, backup, an...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
pwSafe 3.1 - Secure password management...
pwSafe provides simple and secure password management across devices and computers. pwSafe uses iCloud to keep your password databases backed-up and synced between Macs and iOS devices. It is... Read more
StatsBar 1.8 - Monitor system processes...
StatsBar gives you a comprehensive and detailed analysis of the following areas of your Mac: CPU usage Memory usage Disk usage Network and bandwidth usage Battery power and health (MacBooks only)... Read more
Path Finder 6.5.5 - Powerful, award-winn...
Path Finder is a file browser that combines the familiar Finder interface with the powerful utilities and innovative features. Just a small selection of the Path Finder 6 feature set: Dual pane... Read more
QuarkXPress 10.2.1 - Desktop publishing...
With QuarkXPress, you can communicate in all the ways you need to -- and always look professional -- in print and digital media, all in a single tool. Features include: Easy to Use -- QuarkXPress is... Read more
Skype 6.19.0.450 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
Capo 3.1.2 - Slow down and learn to play...
Capo lets you slow down your favorite songs so you can hear the notes and learn how they are played. With Capo, you can quickly tab out your songs atop a highly-detailed OpenCL-powered spectrogram... Read more
VueScan 9.4.41 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more

Latest Forum Discussions

See All

Modern Combat 5 Gets a Major Multiplayer...
Modern Combat 5 Gets a Major Multiplayer Update Posted by Jessica Fisher on September 2nd, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Alien Creeps TD Review
Alien Creeps TD Review By Jennifer Allen on September 2nd, 2014 Our Rating: :: EXPENSIVE DEFENSESUniversal App - Designed for iPhone and iPad Alien Creeps TD would be a fun if unremarkable Tower Defense game, but its heavy focus on... | Read more »
The Journey Down: Chapter Two Review
The Journey Down: Chapter Two Review By Jennifer Allen on September 2nd, 2014 Our Rating: :: DARK YET ENTICINGUniversal App - Designed for iPhone and iPad It’s a little dark, in every sense of the word, but The Journey Down:... | Read more »
Function Space, a Social Network App for...
Function Space, a Social Network App for Science, Launches on iOS Posted by Ellis Spice on September 2nd, 2014 [ permalink ] | Read more »
Stupidfast – How Taylor Martinez Switche...
How do you make an Endless Running game more than just another Endless Running game? By adding real life prizes to it, of course! That’s the thinking behind StupidFast: a game designed for football enthusiasts, and the brainchild of former college... | Read more »
Little Raiders: Robin’s Revenge Review
Little Raiders: Robin’s Revenge Review By Jennifer Allen on September 2nd, 2014 Our Rating: :: CASUAL RAIDINGUniversal App - Designed for iPhone and iPad Combining simple combat with village building is a potent combination for... | Read more »
Treasure Tombs: Ra Deal Coming from Bulk...
Treasure Tombs: Ra Deal Coming from Bulkypix and Dark Tonic This Fall Posted by Jessica Fisher on September 2nd, 2014 [ permalink ] Dark Tonic and | Read more »
Pirate Bash Review
Pirate Bash Review By Nadia Oxford on September 2nd, 2014 Our Rating: :: BAD PIRATES, GOOD TIMESUniversal App - Designed for iPhone and iPad Pirate Bash’s turn-based battles add an intriguing twist to a typical physics game.   | Read more »
Tiny Tower Vegas Review
Tiny Tower Vegas Review By Jennifer Allen on September 2nd, 2014 Our Rating: :: STEADY DEVELOPMENTUniversal App - Designed for iPhone and iPad Build a huge tower again but Vegas-style in Tiny Tower Vegas.   | Read more »
The Manhattan Project Review
The Manhattan Project Review By Andrew Fisher on September 2nd, 2014 Our Rating: :: ROCKET SCIENCEUniversal App - Designed for iPhone and iPad The Manhattan Project offers a great Euro-style gameplay experience, but it is totally... | Read more »

Price Scanner via MacPrices.net

Apple refurbished iPads available for up to $...
Apple is offering Certified Refurbished iPad Airs for up to $140 off MSRP. Apple’s one-year warranty is included with each model, and shipping is free. Stock tends to come and go with some of these... Read more
Are We Now In The Post-Post-PC Era?
A longtime and thoroughgoing laptop aficionado, I was more than a little dismayed by Steve Jobs’s declaration back in 2010 when he sprang the iPad on an unsuspecting world. that we’d entered a “post-... Read more
PC Outlook Improves, But 2014 Shipments Still...
According to the International Data Corporation (IDC) Worldwide Quarterly PC Tracker, worldwide PC shipments are expected to fall by -3.7 percent in 2014. To hat’s actually an improvement from the... Read more
IDC Lowers Tablet Sales Projections for 2014...
Following a second consecutive quarter of softer than expected demand, International Data Corporation (IDC) has lowered its worldwide tablet plus 2-in-1 forecast for 2014 to 233.1 million units. The... Read more
Apple now offering refurbished 21-inch 1.4GHz...
The Apple Store is now offering Apple Certified Refurbished 21″ 1.4GHz iMacs for $929 including free shipping plus Apple’s standard one-year warranty. Their price is $170 off the cost of new models,... Read more
Save $50 on the 2.5GHz Mac mini, on sale for...
B&H Photo has the 2.5GHz Mac mini on sale for $549.99 including free shipping. That’s $50 off MSRP, and B&H will also include a free copy of Parallels Desktop software. NY sales tax only. Read more
Save up to $300 on an iMac with Apple refurbi...
The Apple Store has Apple Certified Refurbished iMacs available for up to $300 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. These are the best prices on... Read more
The Rise of Phablets
Carlisle & Gallagher Consulting Group, a businesses and technology consulting firm focused solely on the financial services industry, has released an infographic depicting the convergence of... Read more
Bad Driver Database App Allows Good Drivers t...
Bad Driver Database 1.4 by Facile Group is a new iOS and Android app that lets users instantly input and see how many times a careless, reckless or just plain stupid driver has been added to the... Read more
Eddy – Cloud Music Player for iPhone/iPad Fre...
Ukraine based CapableBits announces the release of Eddy, its tiny, but smart and powerful cloud music player for iPhone and iPad that allows users to stream or download music directly from cloud... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.