Evolutionenabled applicationprogramming interfaces

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Evolution-enabled application-programming
interfaces

• Ralf Lämmel
• Data Programmability Team
• Microsoft, Redmond

Edited for online publication
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API asbestos and its remedy
C code for window creation in pre-.NET HWND
hwndMain CreateWindowEx( 0, "MainWinClass",
"Main Window", WS_OVERLAPPEDWINDOW WS_HSCROLL
WS_VSCROLL, CW_USEDDEFAULT, CW_USEDEFAULT,
CW_USEDDEFAULT, CW_USEDEFAULT, (HWND)NULL,(HMENU
)NULL, hInstance, NULL) ShowWindow(hwndMain,
SW_SHOWDEFAULT) UpdateWindow(hwndMain)
.NET version Form form new Form() form.Text
"Main Window" form.Show()
Source of the term software asbestos Klusener,
Lämmel, Verhoef Architectural modifications to
deployed software, 2005, Science of Computer
Programming
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Table of contents

• Call to arms
• More examples
• Categorization
• Techniques
• Show stoppers

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Evolutionary API transformationsWhy is that a
worthy research challenge?

• Improve quality of APIs.
• Support effective obsoletion.
• Decrease platform complexity.
• Orthogonal to model-driven xyz.
• Improve productivity of developers.

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API evolution samples

• CodeDom program generation
• Xml.Schema XML schema processing
• DOM vs. XML binding API-fication

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API asbestosMy first .NET program
Use CodeDom API for program generation
CodeCompileUnit compileUnit new
CodeCompileUnit() // ... build some cool code
objects CSharpCodeProvider provider new
CSharpCodeProvider() ICodeGenerator gen
provider.CreateGenerator() IndentedTextWriter
tw new // create a text writer
gen.GenerateCodeFromCompileUnit(compileUnit,
tw, new CodeGeneratorOptions())

• Sigh!
• Main.cs(,) warning CS0618
• 'System.CodeDom.Compiler.CodeDomProvider.CreateGen
  erator() is obsolete.

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Typical developer support
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Elimination of the obsolete pattern
CodeCompileUnit compileUnit new
CodeCompileUnit() // ... build some cool code
objects CSharpCodeProvider provider new
CSharpCodeProvider() // ICodeGenerator gen
provider.CreateGenerator() IndentedTextWriter
tw new // create a text writer
provider.GenerateCodeFromCompileUnit(compileUnit,
tw, new CodeGeneratorOptions())
That is, we get rid of the extra generator
object, and directly use the Generate method of
the provider object.
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How to ?
CodeCompileUnit compileUnit new
CodeCompileUnit() // ... build some cool code
objects CSharpCodeProvider provider new
CSharpCodeProvider() // ICodeGenerator gen
provider.CreateGenerator() IndentedTextWriter
tw new // create a text writer
provider.GenerateCodeFromCompileUnit(compileUnit,
tw, new CodeGeneratorOptions())

• Find offending Create calls.
• Get a handle on factory (provider).
• Find all uses of created generator.
• Setup provider itself as generator.

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More API asbestosMy second .NET program
Use Schema object model (SOM) for schema
processing XmlSchema schema new XmlSchema()
// do something cool with the schema
schema.Compile( new ValidationEventHandler( Val
idationCallbackOne))

• Sigh!
• Main.cs(,) warning CS0618 'System.Xml.Schema.X
  mlSchema.Compile(System.Xml. Schema.ValidationEven
  tHandler)' is obsolete 'Use System.Xml.Schema.Xml
  SchemaSet for schema compilation and validation.'

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An attempted modernization
XmlSchema schema new XmlSchema() // do
something cool with the schema XmlSchemaSet
set new XmlSchemaSet() set.Add(schema)
set.ValidationEventHandler new
ValidationEventHandler( ValidationCallbackOne)
// schema.Compile( // new ValidationEventHandler
( // ValidationCallbackOne)) set.Compile()
How to get this right? Is the above guess correct
anyway?
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Deprecated classes, methods, fieldsin Java world
Source Henkel Diwan CatchUp! Capturing and
Replaying Refactorings to Support API
Evolution International Conference on Software
Engineering, 2005
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Burdens implied by API evolution

• API producer
• Upward compatibility
• Extending maintenance
• Investments
• Tools
• Processes
• Documentation
• API consumer
• Re-engineering for eradication
• Complexity due to multiple versions

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An example for API-fication or translation

• Given a C program that accesses XML business
  data through DOM.
• Wanted a converted C program that uses XML
  binding instead.
• Needed (This is the naïve version.)
• The relevant XML schema(s)
• An XML binding technology
• A dedicated C program transformation
• Potentially IDE component

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Untyped (DOM-based) XML functionality
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Typeful XML functionality
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Kinds of API evolution

• Refactoring
• Service introduction
• Service extension
• Service elimination
• Service restriction
• API-fication
• API translation

• Example Replacement of DOM by XML binding
• Refactoring Prepare the introduction of XML
  binding technology
• Translation Replace DOM patterns by
  schema-derived object model
• Extension Inject additional validation
  functionality into the application

Compare to kinds of grammar adaptation Lämmel
Grammar Adaptation, Formal Methods Europe, 2001
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Techniques for API evolution

• Weak and strong obsoletion
• Provision of facades
• Provision of parallel versions
• Migration guides, strategies, wizards
• Byte-code transformations
• Source-code transformations

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What about refactoring?
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Record refactorings on the API developers
siteReplay refactorings on the API users site
Source Henkel Diwan CatchUp! Capturing and
Replaying Refactorings to Support API
Evolution International Conference on Software
Engineering, 2005
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So what?

• We cannot expect in general
• a refactoring suite to be sufficiently
  expressive,
• refactoring to be practical for API developer,
• a change scenario to be semantics-preserving.

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The envisaged transformation framework

• Musts
• Source-code transformation
• Source-code model with high fidelity
• Type analysis, simple DFA/CFA
• Test harness for system under transformation
• Simple feedback mechanisms
• Shoulds
• More advanced user interaction
• More advanced DFA/CFA/effect analyses
• API protocols based on temporal logic
• Security models and other constraints
• Coverage of multiple (all) languages
• Story for 80/20 conversions

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Potential show stoppers

• Language issues
• Incompleteness issues
• Legal issues

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Language issues

• Reflection
• Threads
• Side effects
• Third party frameworks
• Multitude of languages

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Incompleteness issues

• API producer cant convert
• API consumer wont convert

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Legal issues

• How to sell 80/20 solutions?
• Can we promise correctness?
• How to prove correctness to client?
• Development may rely on client code?
• Support may rely on client code?