[mapguide-dev] Metadata

Carsten Hess carsten.hess at autodesk.com
Mon Sep 18 21:37:34 EDT 2006

             Hi all,

	Sorry for joining this discussion so late, I just didn't get around to typing an answer about it sooner. Let me share with all of you the thinking behind why  I chose the signatures for the stubs in the MapGuide Web API the way they are.
	Metadata indeed is a tricky topic - I totally agree with you Jason. There are several standards and most of them are used by a variety of countries but none of them in all. In the US we have this law that asks all government agencies to create FGDC metadata for all data they create. As a result almost everyone in the US is mainly concerned about native FGDC support. 
	If you go to Europe things are different, no one cares about FGDC, they all want ISO ...  Then there is the OGC standard which is gaining popularity...
	So, no matter what standard we would choose to add to the MapGuide API, it would be the wrong one ...
	The only thing they all have in common is that they have a well defined XML schema representation. So if in the MapGuide API we support a general XML schema storage for Metadata we support the most common (if not all) of the standards out there and applications can use the schema information in the XML content to decide what kind of metadata they are  dealing with.
	Then there was the question of whether we should make metadata its own resource type or add a special API like I did. The reason why I chose a new API ultimately is exactly your concern Jason. Storing metadata as a xml  blob may not be the right decision as it won't scale and all resource data is stored as blob.
	Ideally metadata could be indexed in a server so it can be searched quickly. Since we are using DbXML indexing XML files is really easy. Also different MapGuide applications could implement the metadata xml differently and still it would sclae up which is much harder if we were to choose making it a resource type or hardcode a specific metadata standard. 
	So ... anyways ... that is where I am at with my thinking ... what do you all think?

		-----Original Message----- 
		From: Jason Birch [mailto:Jason.Birch at nanaimo.ca] 
		Sent: Monday, September 18, 2006 3:37 PM 
		To: dev at mapguide.osgeo.org 
		Subject: RE: [mapguide-dev] Metadata 

			This comment from the header file:  "The schema of the Content is user 
			driven and not given. Most people will use it for FGDC or ISO Metadata" 
			makes me think that these unstructured entities will be used for storing 
			fully structured GIS metadata. 

			I can understand using freeform XML metadata for file-based storage, so 
			that the data set is a discrete unit.  I am worried, however, that this 
			will be seen as a good approach for a server-based metadata system, and 
			I don't think that it is. 

			Of course, because they are just free-form XML, I guess there is nothing 
			stopping them from referring to other resources for items like contacts, 
			rather than storing the entire FGDC or TC211 document in a blob. 

			Thinking about integration with Map 3D... If there is going to be a 
			metadata editor (which would be GREAT by the way) for creating external 
			XML files for dwgs, shps, sdfs, etc, then these could be parsed on data 

			This item is really high up on my wishlist (I did add it to the osgeo 
			wiki mapguide wishlist document), and I really want to see it done right 
			the first time rather than implementing something that is relatively 
			easy to do but hard for end users to maintain.  Getting metadata buy-in 
			is hard enough without making it difficult for users. 


			-----Original Message----- 
			From: Trevor Wekel [mailto:trevor.wekel at autodesk.com] 
			Sent: Monday, September 18, 2006 14:22 
			To: dev at mapguide.osgeo.org 
			Subject: RE: [mapguide-dev] Metadata 

			Hi Paul, 

			Yes.  You are correct.  The metadata system is intended to store a 
			free-form XML blob for a specific resource.  Resource content documents 
			are similar.  Each resource does have a specific XML schema but as far 
			as the ResourceService is concerned, they are just valid XML blobs. 


			-----Original Message----- 
			From: Paul Spencer (External) 
			Sent: Monday, September 18, 2006 3:13 PM 
			To: dev at mapguide.osgeo.org 
			Subject: Re: [mapguide-dev] Metadata 


			I suspect that the metadata system they are putting in is more in the 
			line of free-form storage system associated with a resource rather than 
			a structured metadata standard (FGDC?) which you seem to think this is. 
			I could be wrong :) 

			For instance, the description of the MapDefinition that you enter in 
			Studio is stored in a metadata tag inside the actual XML representation 
			of the MapDefinition. 

			I think you raise an excellent point, though.  It could be very 
			compelling to have a real metadata capability inside MapGuide. 



			On 18-Sep-06, at 4:17 PM, Jason Birch wrote: 

			> Hi all, 
			> I am concerned that by just storing Metadata as an XML chunk against 
			> resources, that it will be extremely difficult to manage on an 
			> enterprise level.  I may just be getting worked up about something 
			> that has already been considered but... 
			> A good metadata system should store at least organisation and contact 
			> information independently, taking advantage of a relational model and 
			> making maintenance easier.  Meta information stored against data sets 
			> should be composited on the fly into the required metadata standard. 
			> As well, metadata should not be limited to the information stored 
			> directly in MapGuide.  It should be possible to store metadata for 
			> external resources, including those referred to in load procedures. 
			> The metadata for the resultant data would then reference the source 
			> they were derived from. 
			> Hmm.  On the flip side, there should at least be the ability to parse 
			> and load XML metadata in standard formats, such as generated by 
			> ArcGIS. 
			> Jason 
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			|Paul Spencer                           pspencer at dmsolutions.ca   | 
			|Applications & Software Development                              | 
			|DM Solutions Group Inc                 http://www.dmsolutions.ca/| 

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