Models, Programs and Executable UML

23 October 2011

Copyright © 2011 Data Access Technologies, Inc.(Model Driven Solutions)

A division of Data Access Technologies, Inc.

Models, Programs and Executable UMLPresented at the First International Workshop on Combined Object-Oriented Modeling and Programming

Ed Seidewitz


23 October 2011

Models and Programs

What is a model?

A model is a set of statements in a modeling language about some system under study or domain.*

What is a program?

A program is a specification for a computation to be a executed on a computer.

* See Ed Seidewitz, “What Models Mean”, IEEE Software, September/October 2003 for more.


23 October 2011

Contentions

1. All programs are models.

2. Executable UML models are programs.

3. Executable UML models are useful.


23 October 2011

1. All programs are models

A program is a model of the specified computation, abstracting away from the details of how the computation is actually executed on a computer.

A programming language is a modeling language for creating models of execution.

Customer customer = customers.get(customerId);if (customer != null) {

int totalBalance = 0;for (Account account: customer.accounts) {

totalBalance += account.balance;}

}

Customer customer = customers.get(customerId);if (customer != null) {

int totalBalance = 0;for (Account account: customer.accounts) {


}

…and a value called “totalBalance”……and a value called “totalBalance”…

… that is iteratively computed to be the sum of the customer’s account balances.

… that is iteratively computed to be the sum of the customer’s account balances.

There is a customer identified by “customerId”…There is a customer identified by “customerId”…

Java


23 October 2011

OO programs are also domain models

public class Bank {private String bankId;private Set<Customer> customers;private Set<Account> accounts;...

}


}

public class Customer {private String customerId;private Set<Account> accounts;...

}


}

public class Account {private String accountId;private int balance = 0;private Set<Customer> accountOwners;

...}


...}

Classes are intended to reflect domain concepts.Classes are intended to reflect domain concepts.

Fields reflect properties of those concepts…Fields reflect properties of those concepts…

… or relationships with other concepts.… or relationships with other concepts.


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But make implementation commitmentspublic class Customer {

...private Set<Account> accounts = new HashSet<Account>();

public void addAccount(Account account) {if (account != null && !this.accounts.contains(account)) {

this.accounts.add(account);account.addAccountOwner(this);

}}...

}

public class Customer {...private Set<Account> accounts = new HashSet<Account>();

public void addAccount(Account account) {if (account != null && !this.accounts.contains(account)) {

this.accounts.add(account);account.addAccountOwner(this);

}}...

} public class Bank {...private Map<String, Account> customers = new HashMap<String, Customer>();

public Integer totalAccountBalance(String customerId) {Integer totalBalance = null;Customer customer = this.customers.get(customerId);if (customer != null) {

totalBalance = 0;for (Account account: customer.accounts) {


}return totalBalance;

}...

}

public class Bank {...private Map<String, Account> customers = new HashMap<String, Customer>();

public Integer totalAccountBalance(String customerId) {Integer totalBalance = null;Customer customer = this.customers.get(customerId);if (customer != null) {

totalBalance = 0;for (Account account: customer.accounts) {


}return totalBalance;

}...

}

Pick implementation classes for collections.Pick implementation classes for collections.

Deal with bidirectional relationships.Deal with bidirectional relationships.

Choose representations for efficient computation.Choose representations for efficient computation.

Decide on (generally sequential) control structuring.Decide on (generally sequential) control structuring.


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2. Executable UML models are programs

UML began as a notation for models of programs.

But UML 2 has constructs that allow the specification of Turing-complete computation models.

Foundational UML (fUML) provides precise execution semantics.Action Language for fUML (Alf) provides a textual notation.

customer = Customer -> select c (c.customerId == customerId);totalBalance = customer.accounts.balance -> reduce '+';customer = Customer -> select c (c.customerId == customerId);totalBalance = customer.accounts.balance -> reduce '+';

… and a value called “totalBalance” that is sum of the customer’s account balances.

… and a value called “totalBalance” that is sum of the customer’s account balances.

There is a customer identified by “customerId”…There is a customer identified by “customerId”…

Alf


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UML is common for domain modeling


}


}


}


}


...}


...}

The UML model directly corresponds to the program design…

The UML model directly corresponds to the program design…

…but abstracts away from implementation details (like collection classes).

…but abstracts away from implementation details (like collection classes).

It also shows some things implicit in the program, like association composition and bidirectionality.

It also shows some things implicit in the program, like association composition and bidirectionality.


23 October 2011

But diagrams are just notationclass Bank { public bankId: String; public customers: compose Customer[*]; public accounts: compose Account[*];}

class Bank { public bankId: String; public customers: compose Customer[*]; public accounts: compose Account[*];}

assoc AccountOwnership { public accountOwners: Customer[*]; public accounts: Account[*];}

assoc AccountOwnership { public accountOwners: Customer[*]; public accounts: Account[*];} class Account {

public accountId: String; public balance: Integer = 0;}

class Account { public accountId: String; public balance: Integer = 0;}

class Customer { public customerId: String;}

class Customer { public customerId: String;}

A UML class model has semantics independent of its mapping to any other language…

A UML class model has semantics independent of its mapping to any other language…

…which can be notated textually as well as graphically.

…which can be notated textually as well as graphically.

UML isn’t “just pictures”!


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Computation can be modeled, tooclass Bank {

public bankId: String;public customers: compose Customer[*];public accounts: compose Account[*];

public totalAccountBalance(in customerId: String): Integer[0..1] {

customer = this.customers -> select c (c.customerId == customerId);return customer.accounts.balance -> reduce '+';

}...

}

class Bank {public bankId: String;public customers: compose Customer[*];public accounts: compose Account[*];

public totalAccountBalance(in customerId: String): Integer[0..1] {

customer = this.customers -> select c (c.customerId == customerId);return customer.accounts.balance -> reduce '+';

}...

} The underlying semantics are based on data-flow, not an implicit von Neumann architecture.

The underlying semantics are based on data-flow, not an implicit von Neumann architecture.

These actions are inherently concurrent.These actions are inherently concurrent.

…with far fewer implementation commitments.…with far fewer implementation commitments.


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3. Executable UML models are useful

Executable UML models…

…can be tested, because they are programs

…don’t need to be “recoded”, they can be “compiled”

…abstract computation, not machine architecture


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The models are validated in a development/test environment

Programming in UML is just programming

The models are deployed in a production environment

Developers create fully executable models

Developers iteratively execute, test and update the models

…with models provisioned by a platform-specific “model compiler”.

…with models provisioned by a platform-specific “model compiler”.

But at a higher level of abstraction…But at a higher level of abstraction…

Past executable modeling approaches have demonstrated this can be done for

with production quality.


23 October 2011

Resources

• Foundational UML (fUML)– Specification

http://www.omg.org/spec/FUML – Reference Implementation Project

http://www.modeldriven.org/fuml

• Action Language for fUML (Alf)– Specification

http://www.omg.org/spec/ALF – Reference implementation repository

http://lib.modeldriven.org/MDLibrary/trunk/Applications/Alf-Reference-Implementation

• /doc – Latest specification document (currently v1.0 Beta)• /dist – Parser for latest language version

– Alf implementation in Eclipse Papyrus UML toolhttps://bugs.eclipse.org/bugs/show_bug.cgi?id=329865

• Contact: [email protected], http://twitter.com/seidewitz

Models, Programs and Executable UML

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