Evolution-enabled application-programming interfaces
Ralf Lämmel
Data Programmability Team
Microsoft, Redmond
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
Table of contents
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Call to arms
More examples
Categorization
Techniques
Show stoppers
Evolutionary API transformations
Why is that a worthy research challenge?
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Improve quality of APIs.
Support effective obsoletion.
Decrease platform complexity.
Orthogonal to model-driven xyz.
Improve productivity of developers.
API evolution samples
• CodeDom: program generation
• Xml.Schema: XML schema processing
• DOM vs. XML binding: API-fication
API asbestos:
My 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'System.CodeDom.Compiler.CodeDomProvider.CreateGenerator()‘ is
obsolete.
Typical developer support
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.
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());
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Find offending “Create” calls.
Get a handle on factory (provider).
Find all uses of created generator.
Setup provider itself as generator.
More API asbestos:
My 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(
ValidationCallbackOne));
Sigh!
Main.cs(…,…): warning CS0618:
'System.Xml.Schema.XmlSchema.Compile(System.Xml.
Schema.ValidationEventHandler)' is obsolete: 'Use
System.Xml.Schema.XmlSchemaSet for schema compilation
and validation.'
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?
Deprecated classes, methods, fields
in Java world
Source: Henkel & Diwan: “CatchUp! Capturing and
Replaying Refactorings to Support API Evolution”
International Conference on Software Engineering, 2005
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
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
Untyped (DOM-based) XML functionality
Typeful XML functionality
Kinds of API evolution
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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
Techniques for API evolution
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Weak and strong obsoletion
Provision of facades
Provision of parallel versions
Migration guides, strategies, wizards
Byte-code transformations
Source-code transformations
What about refactoring?
Record refactorings on the API developer’s site
Replay refactorings on the API user’s site
Source: Henkel & Diwan: “CatchUp! Capturing and
Replaying Refactorings to Support API Evolution”
International Conference on Software Engineering, 2005
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.
The envisaged transformation framework
Musts
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Source-code transformation
Source-code model with high fidelity
Type analysis, simple DFA/CFA
Test harness for system under transformation
Simple feedback mechanisms
Shoulds
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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
Potential show stoppers
• Language issues
• Incompleteness issues
• Legal issues
Language issues
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Reflection
Threads
Side effects
Third party frameworks
Multitude of languages
Incompleteness issues
• API producer can’t convert
• API consumer won’t convert
Legal issues
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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?
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Semi-automatic transformations for API evolution