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Subject: RE: [emergency] Handling Default ValueLists
Hi, We currently have a mechanism to deploy code lists to a registry and then do schema validation against the code list in the registry. This way you can have control on the registry content AND retain the ability to validate data against those values. I believe that we should go even further and consider having even the specification document in a registry also, as well as any schemas etc. We would be willing to stand up such a registry for EM if others will work with us. By the way we are still looking for others to join the Public Safety and Security subcommittee for GeoWeb 2011.
From: Rex Brooks [mailto:rex.brooks@ncoic.org] I lean toward what Ron and OGC do. My thinking has been that by publishing the value lists separately in a registry we not only provide a default value list, but an example of how to do that as an added benefit for the audience. However the details would need to be worked out. I confess I haven't thought this through in detail, expecting that the time would eventually arrive when it would be required, and I think that time has now arrived. However, I have no problem with Option 2 for the reasons that Don and Lee mention. Hi, The way that “value lists” are starting to be handled in GML communities (e.g. AIXM, CityGML etc) is to use a registry as part of the specification. This holds the value list, is subject to specific access control rules, but can be extended without re-writing the specification. Cheers
From: McGarry, Donald P. [mailto:dmcgarry@mitre.org] I agree…I forgot to mention this in my note, but I am of the opinion that “IF we can enforce it in the schema we SHOULD” From: Lee Tincher [mailto:ltincher@evotecinc.com] My 2 cents: In order to “tightly bind a standard” I believe we should lean toward Option 2. We have seen abuse of the more open options in things like <parameter> in CAP and it has caused a great deal of confusion in the community….so even though Option 2 does add to the complexity I think the pay-off of tightly defining the usage is well worth it…. Thanks, Lee Those who cannot hear an angry shout may strain to hear a whisper - Leonard Nimoy From: McGarry, Donald P. [mailto:dmcgarry@mitre.org] All- I spent some time this morning trying to figure out how to “do” default valuelists in our schemas. It seems like there are two options that I could figure out and we need to make a decision as a TC how to approach this… What we “want” to do is to have a ValueList type in a schema and assign default values to it. Take “DistributionType” in DE 2.0 as an example… You can do 1 or 2: Use your own ValueList Use the default ValueList A default ValueListURI is declared An enumeration is declared that is binded to that ValueListURI with the values you can choose from The problem is that the mechanism to do defaults and restrictions in schemas will allow you to create a restriction on the valuelist type that will default the ValueListURI, but not have a default enumeration, only a value, this doesn’t allow you to do #1. The other problem is that with a default URI and a don’t strongly bind to other another…i.e. I can choose the Option 1: Just define default valuelists in an xml file that we include with the schema & define the default ValueListURI to match the xml file URI and keep the “Values” types as string Pros: Doesn’t add more complexity to schema Developers can just parse the file and use it In some ways more simple (if you ignore the cons) Cons: Not strongly typed – i.e. someone can use the default ValueListURI and put invalid values in Not enforced in the schema – i.e. if someone does do the bullet above, it will validate to the schema Requires an additional file to be distributed with the schema Requires additional and very specific documentation A new “concept” Requires someone to actually read the documentation ;-) Option 2: Define the default valuelist as a strongly typed restriction on the ValueList type, add a choice or abstraction to the schema for elements with a default ValueList that allows for developers to either use the default or their own valuelist Pros: Strongly typed Enforced in the schema Default values will be read in with the schema Single-file solution Matches how KML/GML seem to do things Re-uses existing schema concepts Doesn’t require “conformance” / “business rule” documentation Cons: More complexity in the schema Adds a choice or a layer of abstraction Could be considered more complicated on the surface Thoughts? Don McGarry |
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