The PIF Process Interchange Format and Framework

Jintae Lee, Gregg Yost and the PIF Working Group[1]
Version 1.0
December 22, 1994

Table of Contents
1. Abstract
2. Introduction
3. History and current status
4. PIF
5. Alphabetic Class Reference
6. Extending PIF
7. Appendix A: PIF Syntax
8. Appendix B: An Example PIF File
9. References

5. Alphabetic Class Reference

ACTIVITY
ACTOR
CANNOT-BE-CONCURRENT
CREATES
DECISION
ENTITY
GROUP
MODIFIES
PERFORMS
PREREQUISITE
RELATION
RESOURCE
SKILL
SUCCESSOR
USE

ACTIVITY

Parent classes: ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Component             ACTIVITY                                    Yes             
Precondition          RESTRICTED-KIF-SENTENCE                                     
Postcondition         RESTRICTED-KIF-SENTENCE                                     
Status                SYMBOL                                      Yes

Attribute descriptions:

Component: The subactivities of the activity. For example, if the activity is "Develop Software", its components may include: "Design Software", "Write Code", "Debug Software", and so on. The field is inherited from ENTITY, but here it is restricted so that its values must all be ACTIVITY objects.
Precondition: The conditions that have to be satisfied before the activity can get executed. For example, a precondition of the activity "Run Software" might state that the executable code must be available. Such conditions are expressed using restricted KIF sentences, which are described in Appendix A.
Postcondition: The conditions that are true after the activity is executed. For example, a postcondition of the activity "Run Software" might be that a log file has been updated.
Status: The current state of the activity, for example DONE, WAITING, etc. The values of this field would be domain-specific. It can have multiple values.

Many preconditions and postconditions can be expressed in PIF without using the Precondition and Postcondition attributes of ACTIVITY. For example, the USE relation between an activity A and a resource R implies that one of A's preconditions is that R is available. In general, the Precondition and Postcondition attributes of ACTIVITY should only be used to express conditions that cannot be expressed any other way in PIF. Doing so will maximize the degree to which a process description can be shared with others.

ACTOR

Parent classes: RESOURCE -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Skill                 SKILL                                       Yes

Attribute descriptions:

* Skill: Skills that an ACTOR has.

An ACTOR represents a person, group, or other entity (such as a computer program) that participates in a process.

CANNOT-BE-CONCURRENT

Parent classes: RELATION -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Activity              ACTIVITY                                    Yes

Attribute descriptions:

* Activity: A set of activities that cannot be executed concurrently.

Activities among which this relation holds cannot be executed concurrently. Conversely, activities without this relation among them are assumed to be concurrently executable.

CREATES

Parent classes: RELATION -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Activity              ACTIVITY                                                    
Resource              RESOURCE                                    Yes

Attribute descriptions:

Activity: The activity that creates the resource.
Resource: The resource being created.

DECISION

Parent classes: ACTIVITY -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
If                    RESTRICTED-KIF-SENTENCE                                     
Then                  SUCCESSOR                                   Yes             
Else                  SUCCESSOR                                   Yes

Attribute descriptions:

If: The condition being tested to decide which successor relations to follow.
Then: The successor relations to follow if the condition in the If field holds (that is, if the RESTRICTED-KIF sentence does not evaluate to FALSE).
Else: The successor relations to follow if the condition in the If field does not hold (that is, if the RESTRICTED-KIF sentence evaluates to FALSE).

A DECISION is a special kind of activity that represents conditional branching. If the RESTRICTED-KIF-SENTENCE in its If attribute is satisfied, the next activities in the process flow are those specified in the SUCCESSOR relations in the Then attribute. If not, the next activities are those specified in the SUCCESSOR relations in the Else attribute.

ENTITY

Parent classes: None. ENTITY is the root of the PIF class hierarchy.

Attribute             Value Type                       Multiple Values Allowed    
Component             ENTITY                                      Yes             
Documentation         STRING                                                      
Name                  SYMBOL                                                      
User-Attribute        Quoted list                                 Yes

Attribute descriptions:

Component: Parts of the entity. For example, the components of CHAIR include BACK, SEAT, and LEGS. Similarly, the components of an activity are its subactivities.
Documentation: A description of the entity.
Name: The entity's name.
User-Attribute: This attribute is used to store additional ad-hoc attributes of an object that are not part of its class definition. For example, a process modeling application might allow users to specify additional attributes for ACTOR objects that are not included in ACTOR's PIF definition -- the user might want to add an attribute recording the ACTOR's age, for example. Such additional attributes can be stored in the User-Attribute attribute, which all PIF objects inherit from ENTITY. Another common use is in the Partially Shared Views translation scheme that we propose for interchanging PIF files (see Section 4).
Each value of User-Attribute is a quoted list containing an attribute name and its value(s). For example, a RESOURCE object might have

(User-Attribute `(Color RED GREEN) `(Weight 120))

GROUP

Parent classes: ACTOR -> RESOURCE -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Cardinality           INTEGER                                                     
Member                ACTOR                                       Yes             
Member-Type           CLASS (subclasses of ACTOR                  Yes             
                      only)

Attribute descriptions:

Cardinality: The number of members in the group, if fixed or known.
Member: The individual members of the group.
Member-Type: The type(s) of the individual members of the group. The value type of CLASS for Member-Type refers to the name of a PIF object class. For example, for a group of actors, the value of Member-Type would be the symbol ACTOR. Some groups may extend PIF so that it includes subclasses of ACTOR, for example EMPLOYEE. These subclass names could also appear in the Member-Type attribute.

A GROUP is a group of actors. In PIF, a GROUP is defined to be a special kind of ACTOR. So, for example, one can specify that some activity is performed by a group of people rather than by a single individual. In the future, PIF will probably support multiple inheritance. When it does, GROUP will also be a subclass of a SET type that supports general features of sets of objects. For now, we define GROUP as a subclass of ACTOR that defines a few additional set-related attributes such as Cardinality and Member-Type.

MODIFIES

Parent classes: RELATION -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Activity              ACTIVITY                                                    
Resource              RESOURCE                                    Yes

Attribute descriptions:

Activity: The activity that modifies the resource.
Resource: The resource being modified.

PERFORMS

Parent classes: RELATION -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Actor                 ACTOR                                                       
Activity              ACTIVITY                                    Yes

Attribute descriptions:

Actor: The actor that performs the activity.
Activity: The activity that is performed.

PREREQUISITE

Parent classes: RELATION -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Required-activity     ACTIVITY                                    Yes             
Activity              ACTIVITY

Attribute descriptions:

Required-activity: The activity that is being required.
Activity: The activity that requires the activity in Activity-1.

This relation represents that the activity in Required-activity must be completed before the activity in Activity can begin. The distinction between the PREREQUISITE relation and the SUCCESSOR relation is subtle. PREREQUISITE represents which activities must have been completed before another activity begins, but does not specify precisely when those other activities actually occur. SUCCESSOR represents the flow of control in a process [[arrowhorizex]] that is, the precise order in which activities will actually occur.

RELATION

Parent classes: ENTITY

Attribute descriptions: None, currently.

Currently, RELATION objects have no attributes of their own. PIF uses it as an abstract parent class for more specific relation classes such as USES and PERFORMS.

RESOURCE

Parent classes: ENTITY

Attribute descriptions: None, currently.

A RESOURCE is an entity that is needed in some way to perform an activity. This includes people (represented by the ACTOR subclass in PIF), physical materials, time, and so forth. The PIF Working Group has discussed adding attributes such as Consumable, Sharable and so forth, but so far no decision has been made on what attributes are appropriate.

SKILL

Parent classes: RESOURCE -> ENTITY

Attribute descriptions: None, currently.

A SKILL object represents expertise possessed by actors. As yet, we have not decided on any attributes that are unique to SKILL objects, as the examples we have used in developing PIF make little use of skill information.

SUCCESSOR

Parent classes: RELATION -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Predecessor           ACTIVITY                                                    
Successor             ACTIVITY                                    Yes

Attribute descriptions:

Predecessor: The preceding activity.
Successor: The succeeding activity.

An activity X is a SUCCESSOR of activity Y if X begins after Y completes and no other activities occur between X and Y. A successor relation is unconditional (that is, activity X always immediately follows activity Y) unless it appears as a value of either the Then or Else attribute of a DECISION object. Intuitively, SUCCESSOR relations corresponds to the flow arrows in a process flowchart.

The SUCCESSOR and PREREQUISITE relations are subtly different. See the description of PREREQUISITE for details.

USE

Parent classes: RELATION -> ENTITY

Attribute             Value Type                       Multiple Values Allowed    
Activity              ACTIVITY                                                    
Resource              RESOURCE                                    Yes

Attribute descriptions:

Activity: The activity that uses the resource.
Resource: The resource that the activity uses.