[Mirrored from: http://www.eccnet.com/rif/rifsec1.html]
Electronic Parts Catalogs (EPC's) are used to facilitate the identification of parts information used during the maintenance and repair of equipment.
To support the proliferation of EPC's, the Rail Industry Forum (RIF) Subcommittee on Information Standards (Task Team) contracted with Applied Image Technology (AIT) to develop the Electronic Parts Catalog Exchange Standard (EPCES). The EPCES supports the exchange of text, graphics, parts information and navigation hyperlinks necessary for an EPC application. In addition to deploying EPC's, some recipients of an EPCES exchange will input EPC parts information directly into Railroad purchasing, inventory and accounting applications. AIT, in conjunction with their subcontractor, SoftQuad Inc, (and subsequently AIT contracted with Henderson Software, Inc.) worked with the Task Team to develop the EPCES such that:
The EPCES was developed in three distinct phases with deliverables as follows:
This document, together with The Encoded Parts Catalog, Document Type Definition (DTD) (also provided in electronic format) provide the necessary information for the Rail Industry to implement the EPCES.
The EPCES adheres to accepted International Standards and is patterned after the Air Transport Association (ATA) adaptation of these Standards as follows:
Rail Industry parts catalog information consists of Text; Data (parts information); Images (raster representations of drawings or pictures); and Drawings (vector formatted drawings). Each of these information "objects" has special treatment in the EPCES as follows:
Standard Generalized Markup Language(SGML) is utilized by the
EPCES to encode text, data and provide for the linking of information elements.
SGML, an International Standard, provides an unambiguous syntax for describing
whatever a user chooses to identify within a document. An SGML DTD provides the
structure that categorizes all information in an SGML encoded document. A
tighter DTD structure yields a more reliable information exchange by reducing
ambiguity in encoding documents. In the course of defining the EPCES, it was
agreed to develop a tightly structured DTD by applying the following guidelines:
Tagged Image File Format (TIFF) is the most robust and, today, the most
widely used format for image files. The EPCES specifies ATA's TIFF 5.0 profile
with CCITT Group IV compression for the exchange of bi-tonal images. AIT has
analyzed ATA's TIFF specification and found it to be a subset of TIFF 5.0.
Further, ATA's TIFF specification is a subset of TIFF 6.0. Therefore both TIFF
5.0 and 6.0 products support the EPCES. However, as EPCES is implementing a
subset of TIFF, TIFF compliant products may generate non-EPCES compliant
graphics.
The initial release of EPCES does not specify the encoding of
grayscale or color Images. There are noted difficulties with TIFF 6.0
compression specifications. As Phase II investigation found no integral use of
grayscale or color in Rail Industry EPC's and therefore no immediate requirement
for the exchange of this information, this capability is deferred to a future
release of the EPCES.
The ATA, in part justified by this difficulty, has
determined to utilize the CGM Tile Array capability with Joint Photographic
Exchange Group (JPEG) compression for color and grayscale exchanges.
Significant product availability (therefore, practical implementation) for this
specification is most likely up to one year away.
Therefore, in deferring
an EPCES specification for grayscale and color, the Rail Industry positions
itself to easily adopt the ATA specification when there is sufficient product
support. This strategy provides EPCES the implementation and support benefits
of conforming to all graphic specifications of ATA 2100.
The EPCES specifies Computer Graphics Metafile (CGM) Version 3 for the
exchange of vector information. CGM is arguably the most universally supported
2-D vector interchange format and is the only format allowed for the interchange
of vector graphics information by the ATA.
As mentioned above CGM Version 3
also defines a Tile Array capability for the transmission of grayscale and color
images (this specification is now included in ATA 2100).
There are
two exceptions to the Rail Industry's adaptation of ATA's profile for CGM:
RIF requirements for the EPCES are that users have "point and click" drill down, from major component to minor component information. When an individual part is visually identified, users must have the capability to navigate to that specific part's data. This drill down capability requires that drawings, images, text and data (parts information) be logically interconnected or "linked". SGML encoding and an SGML application, HyTime, support the exchange of these navigational links.
The RIF-EPC DTD, by means of it's hierarchical and by ID/IDREF cross referencing allows linking an information element (drawing, text, data) to another information element, and thus provides drill down capability.
Essential to an EPC application is the capability to select a graphical "call-out"
resulting in a link to information specific to that "call-out". Yet
today, there is no accepted standard for the definition of a "X,Y"
coordinate system necessary to identify a graphic "call-out" (hot
spot).
However,
HyTime, an
SGML application accepted as an International Standard for the creation of
hyperlinked documents and media, easily supports a coordinate system.
Therefore, EPCES defines a coordinate system utilizing HyTime tools specifically
for (and restricted to) the linking of graphics "call-outs" to other
EPCES information.
The EPCES utilizes the DoD Automated Interchange of Technical Information
(MIL-STD-1840B) for the definition of media, labeling and file naming
conventions used in an EPCES exchange. MIL-STD-1840 Draft C, addresses 1840B's
lack of support for alternate media types. Therefore EPCES incorporates the use
of Draft C for the purpose of defining random access media and cartridge tape.
MIL-STD-1840B was chosen over ATA's equivalent standard, MEDSPV61, as
MEDSPV61 does not specify file naming or formatting requirements, but leaves
this up to negotiation between exchanging parties.
There is a high level of correlation between ATA Illustrated Parts Catalog
(IPC) structures and the RIF sample parts catalogs. However, the ATA IPC
standard incorporates more advanced effectivity and revision control information
than evidenced by the RIF samples and has richer markup capability due to a more
stringent style guide for ATA parts catalogs.
Although the ATA IPC DTD was
used as a baseline in the development of the RIF-EPC DTD, the RIF-EPC DTD is
designed to meet the specific requirements of Rail Industry information.
SoftQuad incorporated elements unique to the Rail Industry as well as knowledge
from other sources to develop the RIF-EPC DTD. In the area of drawing and image
specifications, EPCES closely mirrors ATA 2100.
EPCES parallels ATA 2100 in specifying CGM Version 3 with two notable technology exceptions (making EPCES a subset of ATA 2100):
ATA compliant products will exchange EPCES information however, as EPCES is a subset, these products could generate non-compliant EPCES files.
ATA 2100 historically has supported TIFF for the exchange of Raster information. ATA TIFF support was frozen at TIFF 5.0 in favor of implementing CGM Tile Array for the exchange of Raster information. The EPCES specification of TIFF recognizes, as does the ATA, that sufficient vendor support for CGM Tile Array is not yet present. The EPCES TIFF specification is therefore consistent with ATA 2100 as currently implemented. It is expected that EPCES will migrate to the CGM specification for raster information when there is suitable product availability and support.
The RIF will want to continue work that promotes the EPCES Standard. The following suggestions support the maintenance and growth of the EPCES:
Dave Cruikshank Email: dwc@atreides.ca.boeing.com The Boeing Company FAX: 206-544-9608 PO Box 3707, MS 2H-31 Phone: 206-544-8876 Seattle, WA 98124