version； minor version； build number； and revision。 The build number can represent a daily build number； but this is not required。 The revision identifier can represent a random number； but this is not required either。 For my assemblies； I use a revision number of 0； and consider the build number as a patch number。 Visual Basic Express has a built…in mechanism that automatically updates the build and revision numbers。 Here； the asterisk represents the auto…increment： Alternatively； you can use a versioning tool； or you can increment the numbers manually。 The gacutil tool can be executed multiple times with multiple versions； as shown in Figure 12…4。 ■Note For more information about using versioning tools； see this blog entry about auto…incrementing assembly versions： http：//weblogs。asp/bradleyb/archive/2005/12/02/432150。aspx。 Figure 12…4。 An assembly added three times to the GAC with three different versions In Figure 12…4； the assembly VersioningAssembly has been added three times to the GAC with three different versions （1。0。0。0； 1。1。0。0； an d 1。2。0。0）。 With the GAC in this state； an appli cation or another assembly has the option to reference three different versions of the same assembly。 …………………………………………………………Page 358…………………………………………………………… 336 CH AP T E R 1 2 ■ L E A R N I N G A B OU T A PP L I CA TI O N CO N F I G U R AT IO N AN D D Y N A M I C L O AD I N G For an application or assembly to use another assembly； you create a reference。 When the application or assembly is piled； a specific version number of the assembly is referenced。 For example； if a reference to the version 1。1。0。0 of VersioningAssembly is defined； then version 1。1。0。0 of the assembly is loaded。 Adding an Assembly Redirection to a Configuration File Let’s say an application or assembly needs to use a new version of the VersioningAssembly assembly。 To make the application or assembly aware of the new assembly； you update the application or assembly configuration file that references the old assembly。 The configuration file update includes an assembly redirection。 Essentially； what the redirection says is that if a certain version of an assembly is requested； the new version should be loaded。 The following is an example of an assembly redirection。 This configuration file includes an assemblyBinding XML element that defines a collection of assemblies that will be affected。 The collection of assemblies is embedded within the dependentAssembly element。 Within the dependentAssembly element are two child elements： assemblyIdentity and bindingRedirect。 The assemblyIdentity element is used to identity the assembly for which a reference will be redirected。 The bindingRedirect element contains two attributes： oldVersion and newVersion。 The oldVersion attribute identifies the version of the old assembly in the calling assembly or appli cation。 If the specified version of the old assembly is found； the newVersion attribute is used to identify which assembly version should be used instead。 In the example； the old version is 1。1。0。0； and the new version is 1。2。0。0。 The new version has an incremented minor number； indicating a new version of an assembly。 However； the binding redirection does not care whether the newVersion attribute references a newer version or an older version。 The version identifiers identified by the attributes newVersion and oldVersion are just that： identifiers。 …………………………………………………………Page 359…………………………………………………………… CH AP T E R 1 2 ■ L E AR N IN G AB O U T AP P L I CAT I ON CO N F IG U R AT IO N A N D D Y N A M IC L O AD IN G 337 Implementing a Shared Typed Convention…Based Architecture There has been quite a bit of talk in the software munity about convention over configu ration。 Most of this talk began in earnest with the development of Ruby on Rails （http：// rubyonrails。org/）。 Ruby on Rails （Rails for short） is a tool that allows people to very quickly create web sites that provide useful functionality。 Many attribute the success of Rails to its use of convention over configuration。 Some say it is the Ruby language。 Others say it is because Rails is a professional product。 I believe it’s a bination of factors； but the convention over configuration angle does play an important role。 Let’s go back to the problem of loading code dynamically； or for that matter； executing code dynamically。 How much do you expect the programmer to know； and how much do you expect the programmer to guess？ Consider this code： Interface IDefinition End Interface Sub DoIt（ByVal def As IDefinition） " Do Something with def End Sub In the code； you can see an interface IDefinition and a method DoIt（）； with a parameter of type IDefinition。 This creates a contract where to call DoIt（）； you need to pass an instance of type IDefinition。 Is it correct to assume that the dynamic loading of a type can fulfill the cont