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ITIS Phrase Tables, Draft [issued: 04-11-09]
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9
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This is a draft document of the SAE ATIS committee, subject to change.
event-advice
[3]
SEQUENCE OF Event-advice,
event-quantities
[4]
SEQUENCE OF Event-quantities,
event-additional-text
[5]
SEQUENCE OF Event-additional-text
}
The heart of the dual view is that first three elements above fragment of code is considered the same as the
one below, expressed in a more "ATIS centric" way.
.
Event-description ::= CHOICE
{
event-phrase
[1]
TheString,
event-cause
[2]
TheString,
event-advice
[3]
TheString
}
In both cases, a common code list is used. The ERM elements of EventType and EventAdvice map directly
to the 16-bit values used in ITIS. From an ERM perspective the first octet represents which data element
(i.e. EventTypeXXX) is used, while the second octet represents the specific phrase code of the phrase within
the data element. Implementers are urged to review both the ERM message specification in the TMDD
standard and the SAE J2540 standard to fully understand the low level ASN1 tagging issues involved.
Harmonization of these lists will be maintained by the ITE and SAE as a part of the data registry process.
Observe that the ASN1 terms provided in TMDD are in fact the ASN1 value enumerations for each code.
The recommended text for the code is defined by this document. In most cases, it is readily derived from
the ASN1 definition used in ITE.
4
There are several additional restrictions in using the ITIS list in ERM in addition to adherence to the
requirements of SAE J2540 as follows.
Precedence:
The ERM ASN1 found in the adopted ITE TMDD standard is the definitive authority for
ERM message.
Quantities: The ERM requires that quantities used in situation descriptions adopt the standard (usually
metric) quantity definitions and units specified by TMDD, NTCIP, SAE and other ITS standards bodies.
These values can be converted to other units such as miles, pounds, etc., in the end-user application, if
desired. SAE J2540 allows users to send an undefined numerical value followed by a unit phrase, such as
"1000" "pounds". This practice is not recommended when a data element (such as the quantities category)
exists in the message set. Specifically, implementers SHALL NOT use this ability to add values and units
in strings to circumvent the quantities found in a message set.
Sub Set:
The ERM message definition provides most, but not all of the phrases found in ITIS.
Typically these are data elements which in ERM can be expressed somewhere else in the message itself.
The TMDD data element Event-indicators (TMDD #xxx) is an example of this. Such phrases are a part of
ITIS in order to allow the subject concept to be expressed in those messages which do not have an allocated
place for it. The use of ITIS phrases in such an ITE message SHALL be restricted to those elements which
the defining ITE standard allows.
4
Again, local variants in such definitions can be readily established when needed as per J2540 rules.