Introduction to CALS Technical Goal

The number of satellites and the satellite contents is expected to change over time. The CTG is using STEP to define the core model and the architecture into which other standards are linked.

The core model is common to all kinds of product information and it includes structures for defining their components and the relationships between them. Also, the properties of a product are defined. A product may for instance have a shape, a description concerning its maintenance, as well as a number of other aggregated product properties.

The different properties can then be represented using various satellite models. Examples are representations of different shapes by using structured text (SGML), geometry, topology or even video. The different models for property representation can be linked to different kinds of property definitions.

The CTG will be implemented in four phases which are partly overlapping each other. The four phases are:

1. Defining the underlying structure of the technical goal
2. Implementing the core model
3. Implementing prioritised satellites
4. Transferring the parts of the information legacy that are represented by implemented satellite models

During 1997 work has been going on to define details of CTG. The results of this, called CTG version 2, will be published in late 1997 and is aimed at providing guidance for implementations of the CTG.

The architecture of CALS Technical Goal version 2

The CTG version 2 is based on a layered architecture. This kind of architecture is driven by busi-ness needs for information that is highly stable over time and that can also be tailored to fit the ever-changing business processes. The data architecture is a three-layered architecture which consists of the application models, the CTG Specific Models (CSM) and the CTG ontological model (COM). Even if the 'lowest' level of the architecture is not implemented, it is still useful for coordinating the information modelling exercises for defining consistent CTG-specific models.

Application Models

These are models which define the structure of data in a relatively tight context in order to support a specific business situation or a set of specific activities and business processes. Data integrity rules and data aggregation are represented in the model to access and manage information for a specific business situation. They are implemented in a data management environment by derivation of such models into an implementation form, such as the definition structure of a relational database system.

The availability of the data may be derived from an implemented level of the CTG data architecture which may have a wider context, such as from the level of CTG-specific models or from the level of the CTG ontological model. Data may also be created at the application model level and put into an implemented level of the CTG data architecture of wider context.

The application builders in the organization do not need to use or even be aware of the CTG ontological level since they access all information from either the CTG-specific level or the application model level. For the development of models on these levels, especially if information should be shared between applications, it will not be sufficient to understand only the business needs. It is also important to know how concepts in these models are mapped to the CTG ontological model. If there is a 'warehouse' level implemented in the realized architecture the mapping specifications will allow the data to be available whereever it is needed, possibly without the knowledge of the users of the application.

CTG Specific Models

These are models which define data structures for a specific subject area. The context of a model is defined by the need to maintain data integrity and data aggregation of a specific subject area, regardless of the use of the data and definitions in a specific business situation. For example, the context and purpose of a CTG-specific model for "organization" is defined by the need to have a complete specification about organizations, their structures and relationships, regardless of whether a specific business situation requires the complete model or not.

CTG-specific models present a view of the data which is more specific to the requirements of a defense organization. This specific point of view identifies entities, such as products and materiel, which can be understood and used by applications. It is on this level that the core and satellite models are developed; the core model provides a common reference point to which information may be attached, and the satellites provide detailed models for a specific area.

CTG Ontological Model

The CTG ontological model is based on the idea of the "EPISTLE" model and is a data model with practically universal context. This means that the model does not impose any constraints on the data, which can be held in conformance to that model. It is the full responsibility of an application system, which operates at the level of the CTG ontological model, to provide proper populations of the model. The CTG ontological model is suitable for holding data from many business situations and disciplines. This is useful when data must be integrated and consolidated from many business situations for a common purpose, such as the need for data management on products throughout their life-cycle.

The CTG Ontological Model is a model that represents data in a form which exceeds the third normal form, and it has a tendency to describe any piece of information as an object in its own right. From a data model definition view, such models can be assigned to everything and anything as it suites the business situation, in which the data may be used.

Håkan Kårdèn is the managing director of the EuroSTEP Group.