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
$99.02
Apple Inc.
+1.35
MSFT
$43.97
Microsoft Corpora
-0.53
GOOG
$590.60
Google Inc.
+1.58

MacTech Search:
Community Search:

Software Updates via MacUpdate

OS X Yosemite Wallpaper 1.0 - Desktop im...
OS X Yosemite Wallpaper is the gorgeous new background image for Apple's upcoming OS X 10.10 Yosemite. This wallpaper is available for all screen resolutions with a source file that measures 5,418... Read more
Acorn 4.4 - Bitmap image editor. (Demo)
Acorn is a new image editor built with one goal in mind - simplicity. Fast, easy, and fluid, Acorn provides the options you'll need without any overhead. Acorn feels right, and won't drain your bank... Read more
Bartender 1.2.20 - Organize your menu ba...
Bartender lets you organize your menu bar apps. Features: Lets you tidy your menu bar apps how you want. See your menu bar apps when you want. Hide the apps you need to run, but do not need to... Read more
TotalFinder 1.6.2 - Adds tabs, hotkeys,...
TotalFinder is a universally acclaimed navigational companion for your Mac. Enhance your Mac's Finder with features so smart and convenient, you won't believe you ever lived without them. Tab-based... Read more
Vienna 3.0.0 RC 2 :be5265e: - RSS and At...
Vienna is a freeware and Open-Source RSS/Atom newsreader with article storage and management via a SQLite database, written in Objective-C and Cocoa, for the OS X operating system. It provides... Read more
VLC Media Player 2.1.5 - Popular multime...
VLC Media Player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, MP3, OGG, ...) as well as DVDs, VCDs, and various streaming protocols. It... Read more
Default Folder X 4.6.7 - Enhances Open a...
Default Folder X attaches a toolbar to the right side of the Open and Save dialogs in any OS X-native application. The toolbar gives you fast access to various folders and commands. You just click... Read more
TinkerTool 5.3 - Expanded preference set...
TinkerTool is an application that gives you access to additional preference settings Apple has built into Mac OS X. This allows to activate hidden features in the operating system and in some of the... Read more
Audio Hijack Pro 2.11.0 - Record and enh...
Audio Hijack Pro drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio with Audio Hijack... Read more
Intermission 1.1.1 - Pause and rewind li...
Intermission allows you to pause and rewind live audio from any application on your Mac. Intermission will buffer up to 3 hours of audio, allowing users to skip through any assortment of audio... Read more

Latest Forum Discussions

See All

Traps n’ Gemstones Review
Traps n’ Gemstones Review By Campbell Bird on July 28th, 2014 Our Rating: :: CASTLEVANIA JONESUniversal App - Designed for iPhone and iPad Fight mummies, dig tunnels, and ride a runaway minecart to discover ancient secrets in this... | Read more »
The Phantom PI Mission Apparition Review
The Phantom PI Mission Apparition Review By Jordan Minor on July 28th, 2014 Our Rating: :: GHOSTS BUSTEDUniversal App - Designed for iPhone and iPad The Phantom PI is an exceedingly clever and well-crafted adventure game.   | Read more »
More Stubies Are Coming Your Way in a Ne...
More Stubies Are Coming Your Way in a New Update Posted by Jessica Fisher on July 28th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
The Great Prank War Review
The Great Prank War Review By Nadia Oxford on July 28th, 2014 Our Rating: :: PRANKING IS SERIOUS BUSINESSUniversal App - Designed for iPhone and iPad Though short, The Great Prank War offers an interesting and fun mix of action and... | Read more »
Marvel Contest of Champions Announced at...
Marvel Contest of Champions Announced at Comic-Con Posted by Jennifer Allen on July 28th, 2014 [ permalink ] Announced over the weekend at San Diego Comic-Con was the fairly exciting looking Marvel Contest of Champions. | Read more »
Teenage Mutant Ninja Turtles Review
Teenage Mutant Ninja Turtles Review By Jennifer Allen on July 28th, 2014 Our Rating: :: DULL SWIPINGUniversal App - Designed for iPhone and iPad The pizza power is weak when it comes to this Teenage Mutant Ninja Turtles game.   | Read more »
Exploration Focused Puzzle Game Beatbudd...
Exploration Focused Puzzle Game Beatbuddy Set to Make Transition from PC to iOS this September Posted by Jennifer Allen on July 28th, 2014 [ permalink ] | Read more »
PlanetHD
PlanetHD By Nadia Oxford on July 28th, 2014 Our Rating: :: SPACE MADNESSUniversal App - Designed for iPhone and iPad PlanetHD will keep players busy for a while, though its unpredictable physics are a handful to deal with.   | Read more »
This Week at 148Apps: July 21-25, 2014
Another Week of Expert App Reviews   At 148Apps, we help you sort through the great ocean of apps to find the ones we think you’ll like and the ones you’ll need. Our top picks become Editor’s Choice, our stamp of approval for apps with that little... | Read more »
Reddme for iPhone - The Reddit Client (...
Reddme for iPhone - The Reddit Client 1.0 Device: iOS iPhone Category: News Price: $.99, Version: 1.0 (iTunes) Description: Reddme for iPhone is an iOS 7-optimized Reddit client that offers a refreshing new way to experience Reddit... | Read more »

Price Scanner via MacPrices.net

13-inch 2.5GHz MacBook Pro on sale for $1099,...
Best Buy has the 13″ 2.5GHz MacBook Pro available for $1099.99 on their online store. Choose free shipping or free instant local store pickup (if available). Their price is $100 off MSRP. Price is... Read more
Roundup of Apple refurbished MacBook Pros, th...
The Apple Store has Apple Certified Refurbished 13″ and 15″ MacBook Pros available for up to $400 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. Their prices... Read more
Record Mac Shipments In Q2/14 Confound Analys...
A Seeking Alpha Trefis commentary notes that Apple’s fiscal Q3 2014 results released July 22, beat market predictions on earnings, although revenues were slightly lower than anticipated. Apple’s Mac’... Read more
Intel To Launch Core M Silicon For Use In Not...
Digitimes’ Monica Chen and Joseph Tsai, report that Intel will launch 14nm-based Core M series processors specifically for use in fanless notebook/tablet 2-in-1 models in Q4 2014, with many models to... Read more
Apple’s 2014 Back to School promotion: $100 g...
 Apple’s 2014 Back to School promotion includes a free $100 App Store Gift Card with the purchase of any new Mac (Mac mini excluded), or a $50 Gift Card with the purchase of an iPad or iPhone,... Read more
iMacs on sale for $150 off MSRP, $250 off for...
Best Buy has iMacs on sale for up to $160 off MSRP for a limited time. Choose free home shipping or free instant local store pickup (if available). Prices are valid for online orders only, in-store... Read more
Mac minis on sale for $100 off MSRP, starting...
Best Buy has Mac minis on sale for $100 off MSRP. Choose free shipping or free instant local store pickup. Prices are for online orders only, in-store prices may vary: 2.5GHz Mac mini: $499.99 2.3GHz... Read more
Global Tablet Market Grows 11% in Q2/14 Notwi...
Worldwide tablet sales grew 11.0 percent year over year in the second quarter of 2014, with shipments reaching 49.3 million units according to preliminary data from the International Data Corporation... Read more
New iPhone 6 Models to Have Staggered Release...
Digitimes’ Cage Chao and Steve Shen report that according to unnamed sources in Apple’s upstream iPhone supply chain, the new 5.5-inch iPhone will be released several months later than the new 4.7-... Read more
New iOS App Helps People Feel Good About thei...
Mobile shoppers looking for big savings at their favorite stores can turn to the Goodshop app, a new iOS app with the latest coupons and deals at more than 5,000 online stores. In addition to being a... Read more

Jobs Board

Sr Software Lead Engineer, *Apple* Online S...
Sr Software Lead Engineer, Apple Online Store Publishing Systems Keywords: Company: Apple Job Code: E3PCAK8MgYYkw Location (City or ZIP): Santa Clara Status: Full Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Sr. Product Leader, *Apple* Store Apps - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.