Hands On With the Alf Action Language: Making Executable Modeling Even Easier

Hands On With the Alf Action Language
Making Executable Modeling Even Easier
No Magic World Symposium, Allen TX
Ed Seidewitz
Director of Research and Development
nMeta LLC ● http://www.nmeta.us
ed@nmeta.us ● @seidewitz
Copyright © 2017 Ed Seidewitz
23 May 2017

Goals
• To learn the basics of the Alf action language for Executable UML.
• To learn how to use the Alf Plugin for MagicDraw.
• To practice hands-on using Alf with Cameo Simulation Toolkit.

Prerequisites
• Participant
– Basic knowledge of class, activity and state machine modeling
using MagicDraw
– Some experience with model execution using Cameo Simulation
Toolkit
– General familiarity with programming/scripting (particularly in a
language like C++, Java, JavaScript, etc.)
• System (for hands-on exercises)
– MagicDraw 18.4 or 18.5
– Cameo Simulation Toolkit 18.4 or 18.5
– Alf plugin v18.5

4
Installing the Alf plugin
Plugin documentation is available at:
https://docs.nomagic.com/display/ALFP185/Alf+plugin
Under Plugins (no
cost), download/
install the Alf plugin
v18.5 beta.
Select Help ► Resource/Plugin
Manager to open the Resource/
Plugin Manager window.
 Commercial release
planned for v19.0 in
Q4 2017.

Background

Executable UML
Executable UML is a (growing) subset of standard UML that can be
used to define, in an executable, operational style, the structural and
behavioral semantics of systems.
• Foundational UML (structural and activity models)
– http://www.omg.org/spec/FUML
• Precise Semantics of UML Composite Structure (PSCS)
– http://www.omg.org/spec/PSCS
• Precise Semantics of UML State Machines (PSSM)
– http://www.omg.org/spec/PSSM
• Action Language for Foundational UML (Alf)
– http://www.omg.org/spec/ALF
A textual surface representation for UML modeling elements with the
primary purpose of acting as the surface notation for specifying executable
(fUML) behaviors within an overall graphical UML model.
Alf Plugin

Why an action language?
• Graphical notations are good for…
Structural models
High-level behavioral models

Why an action language?
• …but not so good for detailed behavior
Full executability requires complete
specification of behavior and
computation. This is often much more
easy to specify using a textual notation.

Why not just use a scripting language?
• Scripting language:
No standard syntactic or semantic integration with UML
• Alf:
Full, standardized syntactic and semantic integration with UML
this.lineItems->remove(item)
this.totalAmount = Subtract(this.totalAmount, item.amount)
ALH.removeValue(self, "lineItems", item);
arguments = ALH.createList();
arguments.add(ALH.getValue(self, "totalAmount"));
arguments.add(ALH.getValue(item, "amount”));
ALH.setValue(self, "totalAmount",
ALH.callBehavior("Subtract", arguments));
Example using the MagicDraw-
specific Action Language
Helper API for JavaScript.

The basic idea: Alf maps to fUML
activity DoSomething(in input: Integer, out output Integer): Integer {
output = A(input);
return B();
}
Alf behavioral notation
maps to fUML activity
models.
The semantics of the Alf notation is
defined by its mapping to fUML

Hands On
Hello World

Create an Alf Project
In the Alf folder,
select the Alf
template.
 The Alf template automatically
loads the Alf Library model and
sets Alf as the default language
for opaque behaviors, actions
and expressions.
Under Other,
select Project
from Template.
Select File ► New Project to
open the project creation window.
Create a Hello
World project.

Create the Hello World activity
Create a
new Activity.
Enter the Alf code in
the Alf editor window.
When the code is
correct, click OK.
Right-click on
the Activity and
select Alf.

Executing the activity
Right click on the
Activity and select
Simulation ► Run.
Set Animation Speed
to the highest level…
…and click
here to run.
Output appears in
the console pane.

Basic Concepts

Assignment as data flow
a = +1;
b = -a;
a = A(a) + B(b);
Local names map to
forked object flows.
Subexpressions are
evaluated concurrently.
A re-assigned local
name actually maps
to a new flow.
 The literal “1” has type
Natural. The expression
“+1” has type Integer. The
expression “A(a) + B(b)” has
type Integer, which is not
compatible with Natural.
The local name a implicitly
gets the type Integer.
Statements map to structured
activity nodes with control flows
to enforce sequential execution.
a = 1;
a = A(a); ✗
type conformance

Using Alf for behaviors
lineItem = new LineItem(product, quantity);
this.lineItems->add(lineItem);
this.totalAmount = this.totalAmount + lineItem.amount;
Method of an operation
this.lineItems = checkOut.items;
Customer_Order.createLink(checkOut.customer, this);
this.datePlace = CurrentDate();
this.totalAmount = lineItems.amount->reduce '+';
this.SubmitCharge(checkOut.card);
Behavior on a state machine
battFrac = battCond / this.maxBattLevel;
gThrottle = Max(accelPos * (1-battFrac), this.maxGThrottle);
eThrottle = Max(accelPos * battFrac, this.maxEThrottle);
Body of an action

Using Alf for expressions
Activity Edge Guards
State Machine Transition Guards

Hands On
Stopwatch

Open the StopWatch sample project
…
Click Samples on
the Welcome Screen
Under Simulation,
choose the StopWatch
sample project.
 Select File ► Save Project As…
to save a local copy of the project
before continuing.

Setup the project for Alf
Remove the existing
Project Usage for
fUML_Library.
Select File ► Use Project ►
Use Local Project to open the
Use Project window.
From the modelLibraries
directory, choose
Alf-Library.mdzip.
Click Finish to
load the library.

Open the StopWatch state machine

Replace the ready state behavior
Open the Specification
window for the ready
state.
Under Entry, change
the Behavior Type to
Opaque Behavior.
 Be sure to select the ready
state as a whole, not just the
line for the entry behavior.

Replace the reset timer activity with Alf code
 Be sure to click on the line
for the entry behavior, not
the entire state.
Right click on the entry
behavior and select Alf.
Enter the code
into the Alf
editor window.
replaced by
 The use of the prefix this
is required to access an
attribute value in Alf.

Show the Alf code on the state machine diagram
Open the Symbol
Properties window for
the ready state.
Set the Opaque
Behavior Display Mode
property to Body.

Replace the Increase time activity with Alf code
replaced by
 The ++ operator
increments its argument.

Executing the StopWatch model
Right click on the
StopWatch class and select
Simulation ► Run.
Start the simulation, then
trigger the start signal.
Output is displayed
in the console tab.
The current state
machine configuration
is animated.

Sequences

Sequences
activity GetReadings(in sensors: Sensor[*]): Integer[*] {
readings = sensors->collect sensor (sensor.reading);
return readings;
}
The input parameter has
an unordered set of
values (by default).
Object flows always carry
ordered sequences of
values.
Values are handled one
by one within the
expansion region.
The read actions
happen concurrently.
The result is a sequence
ordered respective to the
input sequence.
The return parameter
gets an unordered set
of values (by default).
 The Alf on the left could be
written more simply as:
return sensors.reading;
The local name reading
implicitly gets the type Integer
and the multiplicity [0..*].
 Arbitrary sequences cannot
be assigned to local names
with multiplicity [0..1].
reading = -1;
readings = reading;
reading = readings;
Implicitly gets the multiplicity [0..1]
A single value is really just a
sequence of length 1.
✗ multiplicity conformance

Null as the empty sequence
A LiteralNull is intended to be used to explicitly model the lack of a value.
In the context of a MultiplicityElement with a multiplicity lower bound of 0,
this corresponds to the empty set (i.e., a set of no values). It is equivalent
to specifying no values for the Element.
null = any [ ] { }
From the UML 2.5 specification (clause 8.2.3):
The Alf interpretation: null is the (untyped) empty sequence
sensors = null;
sensors.readings;
WriteLine(null);
WriteLine(name ?? "no name");
“null” can be assigned to any target with
a multiplicity lower bound of 0.
This is not an error. It is equivalent to
sensors->collect sensor (sensor.reading);
which evaluates to “null”.
 An argument for
a parameter of
multiplicity 1..1
cannot be null.
✗
multiplicity conformance
A null-coalescing expression can be used
to provide a non-null “default value”.

Hands On
Address Book

Create the Address Book project
Create a new project
using the Alf
template, as before.

Create the Address Book class model
Make sure these Entry
attributes are public.
Give this association
end a multiplicity of *.

Create Address Book and Entry operations
This is a constructor operation.
Create it in the usual way, and then
apply the standard Create stereotype.

Create the Entry constructor method
Right click on the Entry
operation and select
Create Method ►
Behavior to open this
selection window.
Choose either
Activity or
Opaque Behavior.
Right click on the
Entry operation again
and select Alf to open
the Alf editor.
Enter the Alf code to
initialize an Entry.

Create Address Book operation methods
Create methods for
the AddressBook
operations, and then
enter the Alf code
shown for them.
 A select expression is used to filter
a sequence based on a condition.
The index [1] ensures that at most
one value is selected.
 This expression will return either a
single value or null, as required by
the return multiplicity of 0..1.
 The constructor
operation is used when
creating an instance of
the Entry class.
 The braces { } are
required in if statement
clauses in Alf.

Test the Address Book model
Create an
AddressBookTest
activity with the
Alf code below.
Run the activity
and see if it works!
 A class can also be instantiated without
a constructor, as in new AddressBook().
 The ?? (null-coalescing) operator is
used here because get has return
multiplicity 0..1 and the + operator
requires argument multiplicity 1..1.

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