Ad/2010-08-01 Concrete Syntax for a uml action Language for Foundational uml (Alf) Second Revised Submission

Property Management Service

First, a guiding principle for Alf is that use of Alf should place little or no restriction on the larger model in which Alf is used. For this example, it should be supposed that the graphical model was created before it was decided to use Alf to specify activities for operation methods, so Alf had no influence on the stylistic choices for the model. For example, the following modeling capabilities used in the example model go beyond what is often used in software-oriented class models, but are not precluded by the use of Alf:

• 
  Names with spaces
  
• 
  Data types
  
• 
  Associations with owned ends
  

• 
  Default values
  
• 
  Derived values
  
• 
  Constructors
  
• 
  Interfaces
  
• 
  Components
  
• 
  Ports, Parts and Connectors
  

1. The Property Management Model

Figure B 106 Property Management Package Diagram

Each of the three packages under Property Management is discussed in turn in the following subsections.

1. Data Model

Figure B -107 gives a simplified data model for property management. Note in general the use of spaces in names. This is allowed in a UML model and is not uncommon in business-oriented data models not primarily driven by an information technology style.

Figure B 107 Property Data Model

1. 
   The Property class models the record of a specific property. A class is used because a property record has the semantics of an object, with an identity and attributes that may change over time. However, the property record is also given a unique domain identifier that is used to externally identify the record.
   
2. 
   Property Acquisition Data and Property Disposition Data are considered to be simply composite attributive data of a property record, without independent identity. They are therefore modeled as data types. The association ends acquisition data and disposition data are owned by Property and are therefore attributes of Property.
   
3. 
   Unlike Property Acquisition Data and Property Disposition Data, Location is a class. It is supposed here that there is a problem domain concept of an identifiable location and that there may be multiple properties at the same location (note the “*” multiplicity on the property association end). The association Property Location owns both its association ends.
   
4. 
   The Property::status attribute is derived. The derivation constraint is given in OCL as:
   

(acquisition_data -> isEmpty() implies status = pending) and

(acquisition_data -> notEmpty() and disposition_data -> isEmpty()

implies status = acquired) and

(disposition_data -> notEmpty() implies status = disposed)

(Note that underscores are used here to fill in the spaces in the names. The OCL Specification does not seem to disallow spaces in names, but it is not clear how they would parse in the OCL syntax.)

5. 
   The Property class is abstract with two concrete subclasses for Personal Property (property that is movable, like vehicles and furniture) and Real Property (property that is immovable, like land and buildings). The attributes of these subclasses are optional, because their value is not necessarily known until the property is actually acquired (a property record can be established pending acquisition, in order to generate a property identifier with which to track the acquisition).
   

Figure B 108 Property Operations

1. 
   The stereotype «create» is the standard UML notation used to annotate a constructor operation. Note that there is no particular naming convention required (e.g., the name of the constructor does not have to be the same as the name of the class). The Property::identifier and name attributes are required, so values for these are given as arguments to the constructor (the setting of the status attribute, which is also required, is discussed below). However, the constructor operation does not have any return type shown (per the conventions shown in Subclause 9.3.1 of the UML Superstructure), though it has an implicit return type of Property.
   
2. 
   The update status operation is used to update the derived status attribute consistent with its derivation constraint (given earlier). This operation is called by the constructor, but it is also used by the service operations given later.
   

2. Message Model

1. Request Messages

• 
  Property Record Establishment: Create a property record pending acquisition of the property.
  
• 
  Property Acquisition Notification: Add or update the acquisition data for an existing property record. The property status must not be disposed.
  
• 
  Property Record Update: Update the attributes of an existing property record not related to acquisition or disposal. The property status must not be disposed.
  
• 
  Property Disposition Notification: Add or update the disposition data for an existing property record. The property status must be acquired.
  
• 
  Property Record Deletion: Delete a property record.
  
• 
  Property Record Retrieval: Retrieve a property record given the identifier for the property.
  

Figure B 109 Request Message Model

1. 
   All messages are modeled as data types. Messages are always passed by value, not by reference.
   
2. 
   Despite being data types, every message has a sender-assigned identifier. For a request message, the identifier is used to correlate reply messages (see below).
   
3. 
   For the purposes of this example, the different types of properties are identified in the messages using enumerated values, rather than by specialization.
   

2. Reply Messages

Figure B 110 Reply Message Model

1. 
   As with request messages, reply messages are modeled as data types with identifiers. Every reply message also has a request identifier message that identifies the request message to which the reply correlates.
   
2. 
   For the purposes of this example, all requests, if successful, reply by returning a copy of the identified property record. In the case of a record removal, this is a copy of the removed record. (A more realistic model would likely have different reply messages corresponding to different requests.)
   
3. 
   Messages cannot contain object references. Therefore, all relevant data from the location object is composed into the reply message.
   
4. 
   For the purposes of this example, all requests, if failed, reply by returning a generic Error Reply.
   

3. Service Model

Figure B -111 shows the Property Management Service interface. For the purposes of this example, each operation has a simple synchronous request/reply signature. Each operation takes a single in parameter request of a specific request type and two out parameters. If the request is successful, a success reply is returned in the reply parameter. Otherwise an error reply is returned in the error parameter.

Figure B 111 Property Management Service Interface

Figure B -112 shows the composite structure of the Property Management Service Provider component.

Figure B 112 Property Management Service Provider Component Composite Structure

1. 
   The Property Management Service is used to type a port on the Property Management Service Provider, becoming the single provided interface for the port.
   
2. 
   The Property Management Service Provider has an internal part that directly implements the service. All requests through the port are delegated to this implementation.
   
3. 
   The Property Management Service Provider has another part that is used by the Property Management Service Implementation as a “factory” for creating unique identifiers to give to property records when they are established.
   

Figure B 113 Property Management Service Implementation Class

1. 
   The Property Management Service Implementation class realizes the Property Management Service interface, implementing all its operations. In addition, it adds a private operation used to create reply messages and an association to the generic Identifier Factory class (which is used to connect it to the Identifier Factory part within the Property Management Service Provider component, as shown earlier).
   
2. 
   The Identifier Factory has the simple behavior of generating unique identifiers as sequential integers starting from 0.
   
3. 
   The Impl to Factory association acts as the type of the connector shown in Figure B -112.
   

4. Property Management Service Methods

1. Property

create property

// See Note 1

activity 'create property'(in identifier: String, in name: String) {

this.name = name;

this.'update status'();
}

Notes

1. 
   The namespace clause here includes the fully qualified name for the Property class, uniquely identifying it within the model. Note also the use of single quotes to form names with spaces.
   

update status

acquired or disposed.

*/

activity 'update status'() {

this.status = 'Property Status'::pending; // See Note 2

} else if (this.'disposition data' -> isEmpty()) {

this.status = 'Property Status'::acquired;

} else {

this.status = 'Property Status'::disposed;

}

}

Notes

1. 
   The OCL-like notation “this.'acquisition data' -> isEmpty()” is used to test whether the optional attribute acquisition data is empty.
   
2. 
   The enumeration Property Status is visible in the scope of Property (it is in the same package), so it can be used without import. However, the names of its enumeration literals still need to be qualified.
   

2. Identifier Factory

get next identifier

activity 'get next identifier'(): String {

return IntegerFunctions::ToString(this.'next identifier'++); // See Note 1

}

Notes

1. 
   Alf allows the use of the C-style “++” operator. In this case, the value of next identifier is incremented, but the prior value is returned. That is, the return statement above is mapped as if it were the following equivalent statement sequence:
   

3. Property Management Service Implementation

Note in particular that fUML semantics requires that objects persist between activity invocations at a specific execution locus, unless they are explicitly destroyed. The specification of the Property Management Service takes advantage of this by effectively using the extent of the Property class as a “database” of property records.

create reply

'Property Management Service Implementation';

// See Note 1

private import 'Property Management'::'Message Model'::*;
/** Create a reply message for a given message ID and property object */

activity 'create reply'(in requestId: String, in property: Property):

'Property Management Success Reply' {
propertyData = new 'Property Data' ( // See Note 2

'property identifier' => property.identifier,

'property name' => property.name,

'property status' => property.status,

'property acquisition data' => property.'acquisition data',

'property disposition data' => property.'disposition data' );

propertyData.'property location'

= new 'Location Data' (

'location identifier' => property.location.identifier,

'location address' => property.location.address );

}
if (property instanceof 'Personal Property') {

propertyData.'property type' = 'Property Type'::personal;

propertyData.'property serial number'

= (('Personal Property')property).'serial number';

} else {

propertyData.'property size' = (('Real Property')property).size;

}
return new 'Property Management Success Reply' (

identifier => requestId + "/reply",

'request identifier' => requestId,

property => propertyData );

}

Notes

1. 
   The notation “private import 'Property Management'::'Data Model'::Properties::*” indicates a package import. That is, all the elements of the package 'Property Management'::'Data Model'::Properties are visible within the activity create reply.
   
2. 
   Property Data is a data type, which may only be constructed using a default constructor. The default constructor for a data type provides arguments for each of the attributes of the data type, which are set here using a named-parameter notation.
   

establish

'Property Management Service Implementation';

private import 'Property Management'::'Message Model'::*;

activity establish (

in request: 'Property Record Establishment',

out reply: 'Property Management Success Reply' [0..1],

out error: 'Error Reply' [0..1] ) {
identifier = this.'property identifier factory'.'get next identifier'();

// See Note 1

property =

new 'Personal Property'::'create property'(identifier, request.name);

// See Note 2

} else {

property = new 'Real Property'::'create property'

(identifier, request.name);

}
reply = this.'create reply'(request.identifier, property);

}

Notes

1. 
   The notation “this.'property identifier factory'” maps to a read link action for the association from the Property Management Service Implementation to the Identifier Factory used to generate property identifiers.
   

2. 
   The Property class has the named constructor create property, rather than a default constructor. This is referenced in the constructor invocation by the qualified name “Property::'create property'”. Note that if, instead, the constructor had had the same name as the class, then the constructor could have been referenced simply using the class name, i.e., “new Property(identifier, request.name)”.
   

acquire

'Property Management Service Implementation';

private import 'Property Management'::'Message Model'::*;

activity acquire (

in request: 'Property Acquisition Notification',

out reply: 'Property Management Success Reply' [0..1],

out error: 'Error Reply' [0..1] ) {
property =

Property -> select p (p.identifier == request.'property identifier');

// See Note 1
if (property -> isEmpty()) {

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PAN-001",

'error message' => "Property not found." );

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PAN-002",

'error message' => "Property already disposed." );

property.'acquisition data' = request.'property acquisition data';

// See Note 2

property.'update status'();

}

}

1. 
   The select expression is used to select the elements from a collection that meet the given condition. The type name “Property” here is used as a shorthand for “Property.allInstances()”—that is, the extent of the Property class. Thus, this expression selects the instance of Property (if any) whose identifier equals that given in the request.
   
2. 
   This is an assignment to the acquisition data attribute for property.
   

update

'Property Management Service Implementation';

private import 'Property Management'::'Message Model'::*';

disposition data). Only non-empty values in the update message cause

corresponding attribute updates. Note that none of these updates can

result in a property status change.

*/

activity update (

out reply: 'Property Management Success Reply' [0..1],

out error: 'Error Reply' [0..1] ) {
property = Property -> select p

(p.identifier == request.'property identifier');

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PRU-001",

'error message' => "Property not found." );

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PRU-002",

'error message' => "Property already disposed." );

property instanceof 'Real Property') ||

(request.'size' -> notEmpty() &&

property instanceof 'Personal Property')) {

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PRU-002",

'error message' => "Wrong property type." );
} else if (request.'property location' -> notEmpty() &&

!(Location -> exists loc

(loc.identifier == request.'property location'))) {

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PRU-003",

'error message' => "Location not found." );

if (request.'property location' -> notEmpty()) {

location = Location -> select loc

(loc.identifier == request.'property location');

'Property Location'.createLink(property, location);

}

if (request.'property name' -> notEmpty()) {

}

if (request.'property value' -> notEmpty()) {

}

if (request.'property serial number' -> notEmpty()) {

request.'property serial number';

}

if (request.'property size' -> notEmpty()) {

}
reply = this.'create reply'(request.identifier, property);

}

}

dispose

'Property Management Service Implementation';

private import 'Property Management'::'Message Model'::*;

activity dispose (

in request: 'Property Disposition Notification',

out reply: 'Property Management Success Reply' [0..1],

out error: 'Error Reply' [0..1] ) {
property = Property -> select p

(p.identifier == request.'property identifier');

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PDN-001",

'error message' => "Property not found." );

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PDN-002",

'error message' => "Property not yet acquired." );

property.'disposition data' = request.'property disposition data';

property.'update status'();
reply = this.'create reply'(request.identifier, property);

}

}

delete

'Property Management Service Implementation';

private import 'Property Management'::'Message Model'::*;

activity delete (

in request: 'Property Record Deletion',

out reply: 'Property Management Success Reply' [0..1],

out error: 'Error Reply' [0..1] ) {
property = Property -> select p

(p.identifier == request.'property identifier');

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PRD-001",

'error message' => "Property not found." );

reply = this.'create reply'(request.identifier, property);

property.destroy(); // See Note 1
}

}

Note

1. 
   The expression “property.destroy()” destroys the object property.
   

retrieve

'Property Management Service Implementation';

private import 'Property Management'::'Message Model'::*;

activity retrieve (

in request: 'Property Record Retrieval',

out reply: 'Property Management Success Reply' [0..1],

out error: 'Error Reply' [0..1] ) {
property = Property -> select p

(p.identifier == request.'property identifier');

error = new 'Error Reply' (

identifier => request.identifier + "/error",

'request identifier' => request.identifier,

'error code' => "PRR-001",

'error message' => "Property not found." );

reply = this.'create reply'(request.identifier, property);

}

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