Definition

1. <Feature Edge> instances have the following relationship with <Feature Face> instances.

   1.1	If a <Feature Edge> FE associates to a <Feature Face> FF, then FE shall be part of one of the <Feature Face Ring> components of FF.
   1.2	At feature topology level 3 or higher, if a <Feature Edge> FE is part of any <Feature Face Ring> of a <Feature Face> FF, then FE shall have an association to FF. At lower levels of topology, this relationship may be present, but it is not required.

2. <Geometry Edge> instances have the following relationship with <Geometry Face> instances.

   2.1	If a <Geometry Edge> GE associates to a <Geometry Face> GF, then GE shall be part of one of the <Geometry Face Ring> components of GF.
   2.2	At geometry topology level 3 or higher, if a <Geometry Edge> GE is part of any <Geometry Face Ring> of a <Geometry Face> GF, then GE shall have an association to GF. At lower levels of topology, this relationship may be present, but it is not required.

Rationale

<External Feature Face Ring> is the one-directional topological relationship between a <Regular Feature Face> and the ordered collection of <Feature Edges> that form its outer boundary, so by definition, a <Feature Edge> that belongs to an <External Feature Face Ring> shall border some <Feature Face>.

<Geometry Face Ring> is the one-directional topological relationship between a <Geometry Face> and the ordered collection of <Geometry Edges> that form its outer boundary, so by definition, a <Geometry Edge> that belongs to a <Geometry Face Ring> shall border some <Geometry Face>.

<Internal Feature Face Ring> is the one-directional topological relationship between a <Feature Face> and the ordered collection of <Feature Edges> that form one of its inner boundaries, so by definition, a <Feature Edge> that belongs to an <Internal Feature Face Ring> shall border some <Feature Face>.

Example

1. A <Feature Edge> X is associated with <Feature Faces> A and B. By the <<Edges Bordering Faces>> rule, X shall belong to a <Feature Face Ring> of A and a <Feature Face Ring> of B.

2. A <Geometry Face> GF has a <Geometry Face Ring> containing <Geometry Edge> GE, at geometry topology level 0. GE is not required to associate to GF, although it is allowed to do so.

FAQs

If a given context within a transmittal contains <Feature Topology> but has feature topology level less than 3, can that context legally contain <Feature Edges> that associate to their <Feature Faces>? What about <Geometry Topology>?

Yes, topology of less than level 3 may contain such associations, provided they comply with <<Edges Bordering Faces>>; they're just not required for topology levels less than 3. This applies to both geometry and feature topology.

I, as a consumer, have encountered a <Feature Edge> with an association to a <Feature Face>. Is the <Feature Edge> guaranteed to provide a comprehensive list of all the <Feature Faces> that use the <Feature Edge>? What about <Geometry Topology>?

If the <Feature Edge> appears in a context with feature topology level of 3 or more, then the list of associated <Feature Edges> is guaranteed to be comprehensive. For lower-level topology, the list is required only to comply with <<Edges Bordering Faces>> and is not guaranteed to be comprehensive. This also applies on the <Geometry Topology> side.