# 6.1.1 Differences between Patch and Subrepresentation

 Topic Version 1 Published 09/11/2015 Topic Change History For Standard RESQML v2.0.1

Both patches and subrepresentations are “part of a representation.” The following table explains how the two are different.

Patch

Subrepresentation

Defines or specifies part of a representation. You can define patches then use them to compose/define a representation. If a representation is composed of n patches, each patch SHOULD have an explicit index number from 0 to n-1.

Is a selection of indices (can be nodes) from an existing representation.

Contains information about topology (element index) AND geometry.

Contains information about topology (element index) only, not geometry (it references geometry from the existing representation).

Defines the representation indexing scheme.

Only refers to element indexes of an existing representation.

The sum of all the patches of a representation holds all the elements of the representation.

The sum of all subrepresentations does not (typically) hold all the elements of the representation.

Patches cannot “topologically” overlap. This means that an element (a node, for example) in a patch is not referred to in another patch of the same representation. An element of a multi-patch representation has its indexing defined by two indices:

• the consecutive/successive indexing of its patches
• the indexing of the elements inside the patch

This dual indexing allows us to describe a representation composed of several independent parts.

Several subrepresentations can “topologically” overlap (i.e., the same element index of a representation can be referred to in two or more subrepresentations).

Because of this overlap, you cannot use subrepresentations to describe a representation composed of several independent parts.

All patches composing a representation have the same dimension (e.g., 1D, 2D, 3D) as the representation.

A subrepresentation can have different dimensions (e.g., 1D, 2D, 3D) than the representation on which it is based (e.g., a subrepresentation can be a 2D line created from points belonging to a triangulated surface).

Is NOT an Energistics top-level object (TLO).

IS an Energistics TLO (that is, it has a UUID, inherits from AbstractObject, etc.)