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Persistent Identification

The Persistent ID Component (PID), generates an identifier that is attached to an entity and is retained by the entity from session to session. The identifier is designed to be unique over all sessions of ACIS. The user has great flexibility in controlling the migration of the identifier through ACIS processing. The identifier is attached to an entity by ACIS attributes.

The PID identifier (persistent ID) consists of:

Topics include:

Accessing Persistent ID Data

When an ACIS session is initialized, a base is established for the persistent IDs of this session. The user can control the initialization process by replacing the pid_base_init function with the desired functionality. The default action is as follows:

The persistent ID is attached to an entity by a PID attribute. The PID attribute contains an object of the pid_base class. Only one PID attribute is allowed per entity. The user accesses the persistent ID data of an entity using the following class methods:

get_base_name
Returns the user name of the entity's identifier.
get_time_val
Returns the time of the entity's identifier.
get_index
Returns the index of the entity's identifier.
get_copy_num
Returns the copy number of the entity's identifier.

On the entity level, the following class methods are available:

remove_pid
Removes persistent ID from this entity.
set_next_current_pid
Adds persistent ID to this entity based on the current base for this session, and increments the index.

API Interface

The following APIs are used for PID:

api_pidset

The api_pidset function creates a persistent ID for a given entity, provided one does not already exist. The new identifier is generated from the current session user name and time, and the entity index is incremented by one.

api_pidrem

The api_pidrem function removes the persistent ID from a given entity, provided one exists. No attempt is made to reuse this persistent ID for a subsequent entity. For example, refer to the following sequence of function calls:

  1. api_pidset(A)
    Entity A is given a persistent ID; this ID is associated with index 1.
  2. api_pidrem(A)
    Entity A has no persistent ID (so, no index).
  3. api_pidset(B)
    Entity B is given a persistent ID with index 2 (the ID associated with index 1 is not reused).
  4. api_pidset(A)
    Entity A is given a persistent ID with index 3 (the ID associated with index 1 is not reused).

api_pidget

The function api_pidget returns the pid_base of the given entity, provided one exists. The data can then be manipulated. For example, the following code fragment gets the pid_base for an entity, then prints the PID data of an entity using the pid_base class methods.

const pid_base* P;
api_pidget(Ent, P);
printf(" pid user %s\n", P->get_user());
printf(" pid time %d\n", P->get_time_val());
printf(" pid index %d\n", P->get_index());
printf(" pid copy %d\n", P->get_copy_num());

Customizing PID Functions

The user can control certain PID activities by writing a customized version of the function for the corresponding activity, and then linking this version first. PID has been designed so the user can replace the existing functions with their own versions to provide maximum flexibility and control over the behavior of persistent IDs. The functions that a user may want to customize include:

pid_base_init
Initializes a session.
get_next_current_pid                 
Gets the next persistent ID for this session.
pid_attrib_copy
Copies an entity.
pid_attrib_restore
Restores an entity.
pid_attrib_save
Saves an entity.
merge_owner
Merges an entity.
split_owner
Splits an entity.

For example, the following customized version of the pid_base_init function is used to initialize the persistent ID. The base of the persistent IDs for this session includes the user field, Testing, instead of the session user time and field zero.

#include "pid/pid.hxx"		//set the fields in the base
void pid_base_init(
	pid_base* session_base)	// basis pid for this session
{
// create_pid_base_name is a method of the pid_base class
create_pid_base_name("Testing", base->base_name);
session_base->time_val = 0;
session-index = 0;
session->copy_num = 1;
}

The following are the default actions for the functions:

pid_base_init
Defines the name by the environment variable, USER. The time is the number of seconds since January 1, 1970. The index is set to 0, and the copy number is set to 1.
get_next_current_pid
Determines the name and time by the session_base. The index of the session_base is incremented. The copy number is 1.
pid_attrib_copy
Sets the persistent ID of the copy to be returned from get_next_current_pid.
pid_attrib_restore
Restores the attribute saved with this entity. No attempt is made to prevent duplication of an entity with the same persistent ID if it is restored twice.
pid_attrib_save
Saves the attribute attached to this entity.
merge_owner 
No default action.
split_owner
No default action.

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