interacting domain specific languages
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Developing Interacting Domain Specific Languages
Developing Interacting Domain Specific LanguagesMaster’s thesis
Sander Mak
Center for Software Technology, Universiteit Utrecht
October 25, 2007
Supervisor : Doaitse SwierstraDaily supervision : Bastiaan Heeren
Eelco Visser
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
Outline
1 Introduction
2 DomainModel
3 WebLayer
4 Interaction
5 Reflection
6 Conclusion
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
Domain Specific Language
Advantages:
Increased productivity
Increased quality
Clarity by abstraction
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
Languages?
Why the plural, i.e. DSLs
One-size fits all, monolithicapproaches generally notsuccesful (like 4GLs)
Separation of concerns, and:reusability of DSL in othercontexts
Premise: Technical domains are agood unit of composition
Research questions:
1 Are multiple interacting DSLs feasible?
2 How should interaction be concretized and implemented?
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
Languages?
Why the plural, i.e. DSLs
One-size fits all, monolithicapproaches generally notsuccesful (like 4GLs)
Separation of concerns, and:reusability of DSL in othercontexts
Premise: Technical domains are agood unit of composition
Research questions:
1 Are multiple interacting DSLs feasible?
2 How should interaction be concretized and implemented?
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
Languages?
Why the plural, i.e. DSLs
One-size fits all, monolithicapproaches generally notsuccesful (like 4GLs)
Separation of concerns, and:reusability of DSL in othercontexts
Premise: Technical domains are agood unit of composition
Research questions:
1 Are multiple interacting DSLs feasible?
2 How should interaction be concretized and implemented?
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
Languages?
Why the plural, i.e. DSLs
One-size fits all, monolithicapproaches generally notsuccesful (like 4GLs)
Separation of concerns, and:reusability of DSL in othercontexts
Premise: Technical domains are agood unit of composition
Research questions:
1 Are multiple interacting DSLs feasible?
2 How should interaction be concretized and implemented?
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
The case study
DomainModel Modeling domain data, generatingJPA (similar to Hibernate) implementation
WebLayer Modeling the view side of web-applications,generating Seam/JSF/Facelets
BusinessRules Modeling functionality specific to a domain
Different compilers, one goal: build a complete Java based web-app
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
Goals
Why create DSLs for these domains:
Increase productivityAbstract away from implementation details, focus on domainconcepts (also gives more clarity)Java frameworks are (inherently?) verbose
Increase qualityDynamic, interpreted mechanisms subvert static safety of Java codeReport domain specific errors
What is explicitly not our goal:
creation of production quality languages,unleashing every bit of power of target frameworks
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
Goals
Why create DSLs for these domains:
Increase productivityAbstract away from implementation details, focus on domainconcepts (also gives more clarity)Java frameworks are (inherently?) verbose
Increase qualityDynamic, interpreted mechanisms subvert static safety of Java codeReport domain specific errors
What is explicitly not our goal:
creation of production quality languages,unleashing every bit of power of target frameworks
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Introduction
Goals
Why create DSLs for these domains:
Increase productivityAbstract away from implementation details, focus on domainconcepts (also gives more clarity)Java frameworks are (inherently?) verbose
Increase qualityDynamic, interpreted mechanisms subvert static safety of Java codeReport domain specific errors
What is explicitly not our goal:
creation of production quality languages,unleashing every bit of power of target frameworks
Intended use
To create data-intensive web-applications, within confines ofcompany guidelines.
‘You can’t be everything to everyone,so be something for someone’
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
DomainModel language
Language for defining persistent domain (or data) models
Essential features:
Concise definition of concepts (entities)
Generates JPA implementation (standardized library)
Encodes domain specific technical knowledge (e.g. object identity)
Allows for domain specific semantic checking
May be used in combination with different DSLs
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
Types: Value, Extended (validated), Concept, List, Enumeration
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
Types: Value, Extended (validated), Concept, List, Enumeration
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
Types: Value, Extended (validated), Concept, List, Enumeration
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
Types: Value, Extended (validated), Concept, List, Enumeration
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
Types: Value, Extended (validated), Concept, List, Enumeration
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
Associations: Value, Reference, Composite
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
Associations: Value, Reference, Composite
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
Associations: Value, Reference, Composite
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
DomainModel annotations
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
DomainModel annotations
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
DomainModel annotations
Compiling a DomainModel concept
Definition BlogEntry results in BlogEntry.java, apersistable JPA entity:
268 LoC
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > DomainModel
Concept definition
concept BlogEntry {title :: String (name, required)abstract :: Stringcontents :: String (required)user -> Userdate :: Date (name)tags -> [Tag]replies <> [Reply]category :: {"Technical" : TECH, "Other" : NONTECH}trackback :: URL
}
DomainModel annotations
Q: Isn’t DomainModel almost the same as UML Class diagrams?
A: Yes!
We even ’borrowed’ some of the association symbols
’−>’ for references’<>’ for composites
That way, prior UML knowledge helps when usingDomainModel
Theoretically, a UML class diagram could serve as input forthe DomainModel compiler (if only we had a UMLfront-end)
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
WebLayer language
Language for defining pages (views) in web-app
Essential features:
Works seamlessly with DomainModel definitions
Abstracts away from the Seam framework and Java intricacies
Strongly typed
Explicit, checked data-flow between pages
Generic constructs
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
WebLayer compiler
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}
Multiple page definitions in one file, starting with a header:
weblayer blog
using domainmodel blog
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Page definition
page ViewBlog(BlogEntry be, User u){var Reply r
header(be.title + " (written on " + be.date + ")")text(be.contents)table Tag t in be.tags { "Assigned tags" -> t.tagName }
"Reply to this post:"form( input(r)
action( "Add reply", r.user = u; be.replies.add(r); be.save())
)
text("Replies for post " + be.title + " :")for Reply r in be.replies { show(r) }navigate("Home", Blog(u))
}
Ideas for extension
Query language
Partial page abstraction
Parameterized, reusable actions
...
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > WebLayer
Issues
Layout is more or less fixed
Example: every page element is placed beneath each otherWe don’t want to replicate all of HTML inside WebLayerPartial solution: embed generated page in freely editable templateFor the rest: make assumptions, although compiler becomes morespecific
Editing lists
Our solution is specific and ad-hoc
Action language
Why not, for example, embed Java?
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Interaction
DSL Interaction
We can use DomainModel constructs within WebLayer, but how doesthis interaction work?
Goals
Interaction must be intuitive to DSL user
Languages must be as separate as possible
For the sake of reusability
Generated code must statically link
Our solution
Separate compilation for each DSL, communicating essentialinformation through interface files.
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Interaction
DSL Interaction
We can use DomainModel constructs within WebLayer, but how doesthis interaction work?
Goals
Interaction must be intuitive to DSL user
Languages must be as separate as possible
For the sake of reusability
Generated code must statically link
Our solution
Separate compilation for each DSL, communicating essentialinformation through interface files.
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Interaction
DSL Interaction
We can use DomainModel constructs within WebLayer, but how doesthis interaction work?
Goals
Interaction must be intuitive to DSL user
Languages must be as separate as possible
For the sake of reusability
Generated code must statically link
Our solution
Separate compilation for each DSL, communicating essentialinformation through interface files.
Separate compilation illustrated
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Interaction
Interface files
DSL compiler emits interface file. We chose ATerms as genericrepresentation format.
Interface characteristics
Aggregates information
Contains disambiguated information
Contains linking information (types, hooks)
Written interface guarantees a consistent, checked module to bepresent
One way to view interface file mechanism is as cache for compileroperations
Issues: explicit vs. implicit interface, cyclic dependencies betweenDSLs
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Interaction
Interface files
DSL compiler emits interface file. We chose ATerms as genericrepresentation format.
Interface characteristics
Aggregates information
Contains disambiguated information
Contains linking information (types, hooks)
Written interface guarantees a consistent, checked module to bepresent
One way to view interface file mechanism is as cache for compileroperations
Issues: explicit vs. implicit interface, cyclic dependencies betweenDSLs
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Interaction
Interface files
DSL compiler emits interface file. We chose ATerms as genericrepresentation format.
Interface characteristics
Aggregates information
Contains disambiguated information
Contains linking information (types, hooks)
Written interface guarantees a consistent, checked module to bepresent
One way to view interface file mechanism is as cache for compileroperations
Issues: explicit vs. implicit interface, cyclic dependencies betweenDSLs
Q: Why cache, are these operations so expensive?
A: No, not at all. The issue is that the importing compilerotherwise needs to know how to perform these operations. Wedon’t want that, since it breaks our notion of modular interactinglanguages!
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Interaction
Interface files
DSL compiler emits interface file. We chose ATerms as genericrepresentation format.
Interface characteristics
Aggregates information
Contains disambiguated information
Contains linking information (types, hooks)
Written interface guarantees a consistent, checked module to bepresent
One way to view interface file mechanism is as cache for compileroperations
Issues: explicit vs. implicit interface, cyclic dependencies betweenDSLs
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Reflection
Does this approach really work?
Promises of model driven software development:
Gain productivity
Gain quality
... so do we live up to this expectation?
Productivity:1 The factor ∼14 increase in LoC seems to be typical2 DRY: refactoring in DSL code is much easier3 Start-up costs manageable
Quality:1 DSL Type checker guarantees correctness of dynamic
constructions (and there’s much of that in Java web frameworks!)2 Typed, explicit dataflow between pages3 Concrete example: guaranteed prevention of cross-site scripting
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Reflection
Does this approach really work?
Promises of model driven software development:
Gain productivity
Gain quality
... so do we live up to this expectation?LoC metrics - Blog example
DSL Source Generated code
DomainModel 45Java 801XML 22
WebLayer 110Java 841
XML/Facelets 501XML 48
Totals 155 2213 ∼ ×14
Productivity:1 The factor ∼14 increase in LoC seems to be typical2 DRY: refactoring in DSL code is much easier3 Start-up costs manageable
Quality:1 DSL Type checker guarantees correctness of dynamic
constructions (and there’s much of that in Java web frameworks!)2 Typed, explicit dataflow between pages3 Concrete example: guaranteed prevention of cross-site scripting
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Reflection
Does this approach really work?
Promises of model driven software development:
Gain productivity
Gain quality
... so do we live up to this expectation?
Productivity:1 The factor ∼14 increase in LoC seems to be typical2 DRY: refactoring in DSL code is much easier3 Start-up costs manageable
Quality:1 DSL Type checker guarantees correctness of dynamic
constructions (and there’s much of that in Java web frameworks!)2 Typed, explicit dataflow between pages3 Concrete example: guaranteed prevention of cross-site scripting
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Reflection
Does this approach really work?
Promises of model driven software development:
Gain productivity
Gain quality
... so do we live up to this expectation?
Productivity:1 The factor ∼14 increase in LoC seems to be typical2 DRY: refactoring in DSL code is much easier3 Start-up costs manageable
Quality:1 DSL Type checker guarantees correctness of dynamic
constructions (and there’s much of that in Java web frameworks!)2 Typed, explicit dataflow between pages3 Concrete example: guaranteed prevention of cross-site scripting
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Reflection
Drawbacks of our approach
Every semantic check must be written from scratch
For each DSL
Type checking, resolving symbolic references, and so on
Fortunately, we can get very specific with our checks andassociated messages
Module system must be written from scratch
This might be solved generically (parameterizing over interfacedefinitions), though we have not researched this
What are the semantics of our DSLs?
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Reflection
Drawbacks of our approach
Every semantic check must be written from scratch
For each DSL
Type checking, resolving symbolic references, and so on
Fortunately, we can get very specific with our checks andassociated messages
Module system must be written from scratch
This might be solved generically (parameterizing over interfacedefinitions), though we have not researched this
What are the semantics of our DSLs?
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Reflection
Drawbacks of our approach
Every semantic check must be written from scratch
For each DSL
Type checking, resolving symbolic references, and so on
Fortunately, we can get very specific with our checks andassociated messages
Module system must be written from scratch
This might be solved generically (parameterizing over interfacedefinitions), though we have not researched this
What are the semantics of our DSLs?
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Reflection
Alternative approaches
Embedded DSLs
Asynchronous, runtime linking of generated code (independentcode generation)
Larger role for the IDE
Long-term: active libraries and a universal language
Realistically, this probably never happens
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Reflection
Alternative approaches
Embedded DSLs
Asynchronous, runtime linking of generated code (independentcode generation)
Larger role for the IDE
Long-term: active libraries and a universal language
Realistically, this probably never happens
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Conclusion
Demonstration
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Conclusion
Topics not discussed... but interesting nevertheless
1 Actual implementation details of compilers
Implemented using Stratego/XT toolkit
2 BusinessRules interface definition
To overcome limitations of WebLayer action language in multipleDSL style
3 Interaction with GPL code
Necessary for real-world adoptation, but how to implement it?
4 Much more context and related work
... my thesis will be available shortly
Center for Software Technology Sander Mak
Developing Interacting Domain Specific Languages > Conclusion
Concluding remarks
Interacting DSLs indeed feasible
Especially suited for layered architectures (like web-applications)DSLs encode principled usage of frameworks and frameworkinteraction
Interaction implemented through interface files
Separate compilation allows for reuse of DSLsImplicit interface may be a limiting factor
DSLs for technical domains are a serious option for a company topursue, with demonstrated advantages, but also requiring considerableeffort.
Center for Software Technology Sander Mak
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