Real-Time System Management Information Program Data Exchange Format Specification
4. Design Reference
Section 4 of this document contains references to design elements of existing standards that fulfill the requirements of Section 3 Functional Requirements. Therefore, the design is not included in this document, but rather exists in the various standards referenced to fulfill the requirements defined in this DXFS. As such, this section is entitled a Design Reference.
4.2 Requirements Traceability Matrix (RTM)
For the purposes of tracing a requirement to its design elements this section provides four (4) Requirements Traceability Matrices, one for each of the standards whose design elements and data concepts are used to fulfill one of more requirements of the DXFS. Annex B, contained in a separate volume, contains the RTMs for the TMDD, SIRI standard, TCIP, and for the OASIS CAP standard.
4.2.1 Requirement ID and Requirement
The RTMs contain columns titled Requirement ID, and Requirement, which reference a DXFS requirement. The Requirement ID is the paragraph identifier as shown in Section 3, and the Requirement is the paragraph title.
4.2.2 Data Concept Type (DC Type)
A column in the RTM describes the data concept type that fulfills a particular requirement. Data concept types are described below.
- Dialog – The dialog data concept describes the sequence or conditions for information exchanges between a center and other centers. The dialog rows are shown in bold to help the reader identify where a sequence of messages, accompanying data-frames and data-elements beings.
- Message – a data concept to describe the message sent from an external center to an owner center.
- Data-frame – a data concept to describe a portion of a message that may contain other data-frames and data-elements.
- Data-element – a data concept that cannot be broken down into smaller units. A data-element is generally a text string, number, or enumeration, with a set of value and/or size constraints.
The data concept name, data concept identifier, and data concept class name columns are used to identify the design element in one of the four standards documents referenced by this DXFS: TMDD, SIRI, TCIP, or OASIS CAP. As a point of clarification, the DC ID is a look-up reference to allow easy navigation into the referenced standard, and is usually a paragraph identifier. The TMDD, for example, is structured such that a paragraph in the design volume references a generic type name, e.g., 3.4.14.32 Link-speed-limit. The ‘3.4.14.32’ is the Data Concept ID, and the ‘Link-speed-limit’ is the Data Concept Class Name. Several data concepts, or instances, may be of class, or type, Link-speed-limit, for example, speed-limit, and speed-average. Because a message may contain several data concept instances of a particular class, the RTM shows the data concept instance name. Several data concept instances may be included in a TMDD message that are of class Link-speed-limit. For example, the LinkStatusMsg (Link Status Message) contains speed-limit and speed-average.
4.2.4 Comment
A comment column is included to capture any additional information the author feels may benefit a reader.
4.2.5 RTM Table Selection
The RTM table that is selected for definition of data concepts depends upon the requirements selected when the NRTM is completed for a deployment. In the case of requirements that map to the TMDD standard (Table B-1 in Annex B) or requirements that map to OASIS CAP (Table B.4 in Annex B) there is a unique mapping of requirements to the data concepts in the tables. In the case of requirements mapping to transit related data concepts, the mapping is not unique, but will require the agency make a choice between the use of TCIP or SIRI as the source of the data concepts. The decision of which standard to employ is left to individual agencies. A set of considerations regarding which standard to choose are provided in Section 4.2 of the DXFS Implementation Guide.
