An ID model defines the designations for object or design part IDs (identities) and ultimately helps determine which basic information will be registered for the object or design part. Each ID model has a set of primary and secondary ID fields. An object ID model consists of some or all of the 10 primary and 10 secondary identity fields. A design part ID model consists of some or all of the 5 primary and 5 secondary ID fields. When the ID model is connected to a design object or design part class, the unique ID of all objects or design parts in the class share that ID model.
ID separators divide the different sections of the object and design part IDs making them easier to read.
There are two ways to register an ID model. The first is to define the primary and secondary ID fields manually. An object ID may be defined for Primary 01, 02 and 03 as follows:
| Primary 01 | Primary 02 | Primary 03 |
| Department | Type | Number |
The second registration method is to inherit a subset of the model's ID fields from an existing ID model. For example, ID Model B (Piping) could inherit Primary 01-04 from ID Model A (Equipment) and then several more designations could be added, as needed. The designations might appear as follows:
| Primary 01 | Primary 02 | Primary 03 | Primary 04 | Primary 05 | Primary 06 | |
| Model A (Equipment) | System | Code | Number | Parallel Item | ||
| Model B (Piping) | System | Code | Number | Parallel Item | Size | Pipe Class |
Each ID Model is connected to a class in a separate procedure.
Each class can be connected to an ID separator model, which is used to configure the characters that divide the different ID parts. For example, an ID separator model of '-, -, -' would result in an object ID appearing as 10-PU-001. ID separators are optional, but they make object and design part IDs easier to read.
The following rules apply for ID models and separators when discrepancies caused by class changes occur:
For example, an object in the PUMP MISC class has the ID 10-PU-100-1. The ID model of the class has four display fields with the ID separator character, '-'. The object ID composition is as follows:
| Disp1 | Sep | Disp2 | Sep | Disp3 | Sep | Disp4 |
| 10 | - | PU | - | 100 | - | 1 |
If the object's class is changed and the default ID model of the new class contains 3 display fields, the values in the display fields 3 and 4 are combined together into display field 3 by including the existing separator between the two fields. The new object ID composition is as follows:
| Disp1 | Sep | Disp2 | Sep | Disp3 |
| 10 | - | PU | - | 100-1 |
If the new class has 5 ID model display fields, the new object ID composition is as follows:
| Disp1 | Sep | Disp2 | Sep | Disp3 | Sep | Disp4 | Sep | Disp5 |
| 10 | - | PU | - | 100 | - | 1 | - |