The SEDRIS Data Representation Model
APPENDIX B - Constraints
Connected Edge Restrictions

Definition

  1. A <Feature Node> FN has the following relationship with its <Connected Feature Edge> components, if any exist.

    1.1

    For each <Feature Edge> that has FN as a starting node, FN shall have a <Connected Feature Edge> that associates to that <Feature Edge>.

    1.2

    For each <Feature Edge> that has FN as an ending node, FN shall have a <Connected Feature Edge> that associates to that <Feature Edge>.

    1.3

    If FN is neither a starting nor an ending node of a given <Feature Edge>, that <Feature Edge> shall not appear among the associates of any of FN's <Connected Feature Edge> components.

    1.4

    Consequently, for any given <Feature Edge> FE of which FN is a starting or ending node, FE shall appear among the associates of FN's <Connected Feature Edge> components either:

    • once, if FN is FE's starting node and not its ending node,
    • once, if FN is FE's ending node and not its starting node,
    • twice, if FE is a loop.

  2. A <Geometry Node> GN has the following relationship with its <Connected Geometry Edge> components, if any exist.

    2.1

    For each <Geometry Edge> that has GN as a starting node, GN shall have a <Connected Geometry Edge> that associates to that <Geometry Edge>.

    2.2

    For each <Geometry Edge> that has GN as an ending node, GN shall have a <Connected Geometry Edge> that associates to that <Geometry Edge>.

    2.3

    If GN is neither a starting nor an ending node of a given <Geometry Edge>, that <Geometry Edge> shall not appear among the associates of any of GN's <Connected Geometry Edge> components.

    2.4

    Consequently, for any given <Geometry Edge> GE of which GN is a starting or ending node, GE shall appear among the associates of GN's <Connected Geometry Edge> components either:

    • once, if GN is GE's starting node and not its ending node,
    • once, if GN is GE's ending node and not its starting node,
    • twice, if GE is a loop.

Rationale

<Connected Feature Edge> is the one-directional topological relationship connecting a <Feature Node> to the ordered set of ordered collection(s) of <Feature Edge> instances that have it as an endpoint. If there are no such <Feature Edge> instances, then there shall be no <Connected Feature Edge> on that <Feature Node>.

<Connected Geometry Edge> is the one-directional topological relationship connecting a <Geometry Node> to the ordered set of ordered collection(s) of <Geometry Edge> instances that have it as an endpoint. If there are no such <Geometry Edge> instances, then there shall be no <Connected Geometry Edge> on that <Geometry Node>.

Example

  1. Consider a <Feature Edge> A that has distinct starting and ending <Feature Node> instances X1 and X2.

    X1 shall have at least one <Connected Feature Edge> component, which associates to A, and X2 shall have at least one <Connected Feature Edge> component, which associates to A.

  2. Consider <Geometry Node> Y that is not the endpoint of any <Geometry Edge>. If Y is mistakenly created with a <Connected Geometry Edge>, then Y is invalid, since the <Connected Geometry Edge> implies that Y does belong to some <Geometry Edge>.

FAQs

For a loop edge (that is, an edge wherein the same node appears as both the starting and ending node), how many times does the edge appear in that node's <Connected Feature Edge> / <Connected Geometry Edge> lists?

Twice. Non-loop edges would appear only once.

Prev: Colour Table Size. Next: Contained Node Restrictions. Up:Index.

Last updated: May 15, 2003 Copyright © 2003 SEDRIS™