| Re: [railML 2.5] state [message #2753 is a reply to message #2750] |
Mon, 07 June 2021 17:14   |
Thomas Nygreen
Messages: 66
Registered: March 2008
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Dear all,
My conclusion is that we need an explicit "unknown" value, but mostly to be able to override another value explicitly set higher in the hierarchy, e.g. an "operational" state on the whole infrastructure element. I do not agree with Dirk that option 1 changes the default value, because there is no default value. Any information that is not present in a file is unknown, unless a default value has been specified. The recipient may of course make reasonable assumptions, and the reasonable assumption when given an infrastructure model without any explicit state is that it represents an operational infrastructure. This is however not a defined default value, it is just a reasonable interpretation of (gaps in) the data.
When a producing system sends an explicit "unknown" value, it means that the value is actually unknown to the producing system. If a property is missing, on the other hand, it may be known or unknown to the producing system. To a receiving system it does not make much difference, the data is unknown either way, and assumptions may have to be made. The only difference is that with an explicit "unknown", it knows that the value is also unknown to the producing system.
I fully agree with Dirk's reminder about context.
Best regards,
Thomas
Thomas Nygreen – Common Schema Coordinator
railML.org (Registry of Associations: VR 5750)
Altplauen 19h; 01187 Dresden; Germany www.railML.org
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