Meta Model Elements

The Semantic Aspect Meta Model (SAMM) specifies the elements from which an Aspect Model can be built. The following diagram shows the basic building blocks:

aspect meta model

  • A Property represents a named value.

  • An Abstract Entity is a logical encapsulation of a shared concept. It has a number of Properties. An Abstract Entity can extend another Abstract Entity.

  • An Entity is a logical encapsulation of multiple values. It has a number of Properties. An Entity can extend either another Entity or an Abstract Entity.

  • A Characteristic describes a Property’s meaning in the context of the Aspect with information such as its data type, if it is a collection, that a string value is to be interpreted as one of a fixed number of valid states or that a numeric value has an associated physical unit.

  • A Constraint represents a limitation that is applied to another Characteristic (for example on the numeric value range or the maximum length of string).

Characteristics, Constraints and element descriptions, are not part of the data an Aspect sends, but only exist in its model. A number of commonly used Characteristics and Constraints are predefined in the scope of the Semantic Aspect Meta Model, see section Characteristics for more information.

  • An Operation represents an action that can be triggered on the Aspect. Depending on the Aspect, this can, but does not have to, trigger an action on the asset that is represented by the Digital Twin, for example switching a part of a machine on or off.

  • An Event is a model element that represents a single occurence where the timing is important. Assets can for instance emit events to notify other assets in case of special occurences.

  • An Aspect is the root element of each Aspect Model and has a number of Properties, Events, and Operations.

  • A Unit refers to a physical unit, such as metre or degree celsius. A catalog of units are predefined in the scope of the Semantic Aspect Meta Model, see section Units for an in-depth description.

  • A Quantity Kind describes the kind a Unit refers to, such as length or temperature.

  • Quantifiable is the Characteristic that makes use of a Unit. Other Characteristics that are derived from Quantifiable have a Unit as well.

See the sections Attributes that all model elements have and Declaring model elements in section Aspects for hints on using the model elements in an Aspect Model.