Thanks Ian, your points are well taken. I'd like to pursue it further in 
the context of FISH.

TB


Ian Painter wrote:
> Hi Tyler,
>  
> Thanks for the comments. Please find below my response below.
>  
> The issue of complexity is a good one - I would agree with you; if we were considering GML3 - its far too loaded and complex (simple profiles are coming out soon to address this). However, using GML 2 (ISO 19136) you would only need to add just one XML schema file (geometry.xsd) to the MIDAS schema in order to replace the MIDAS geometry encoding with a GML encoding. To go one step further and create MIDAS as a GML2 profile you would need to add just one additional schema file (features.xsd). Apart from that its done. The GML 2 encodings are very simple, easy to use and have the same amount of tag complexity as the current MIDAS schema. I really don't think it would be any more complex than the current schema. 
>  
> On the issue of proprietary. Sorry 'proprietary' is a strong word, I hope I didn't offend or insult anybody involved in MIDAS schemas. Its just that from a spatial point of view MIDAS is a proprietary schema.  MIDAS isn't the first schema that has defined its own spatial types and that's the problem.  I define 'proprietary' as something that requires a custom piece of software to support it. If everybody defines their own points, lines, polygons or use WKT in their own namespace then its going to take a custom piece of software 'hard coded' to each particular schema to support it. In its current form MIDAS will not load with any commercially available GML reader or GIS translator unless a particular vendor changes that software specifically for MIDAS. This will undoubtedly hinder adoption of MIDAS - something that we are seeing in our customer base.
>  
> On addressing your final point. Yes that's always the goal and something people often forget about - its all about removing as many barriers as possible to encourage standard adoption.  I'll see what we can do to create a MIDAS GML profile and post it to the forum for comment. I'm not promising anything quickly, but, I'd like to show the MIDAS community what a few minor tweaks to create MIDAS GML profile could achieve. If it means existing tools will be able to support MIDAS then surely that will be a big help to removing the barriers to MIDAS adoption.
>  
> I hope this all helps.
>  
> Cheers
>  
> Ian
> 
> ________________________________
> 
> From: The Forum for Information Standards in Heritage (FISH) on behalf of Tyler Bell
> Sent: Tue 22/11/2005 21:26
> To: [log in to unmask]
> Subject: Re: [FISH] Feedback on the MIDAS schema
> 
> 
> 
> Dear Ian et al.,
> 
> I'm glad to see an active interest in MIDAS XML and MIDAS spatial.
> 
> I'll note first that GML was considered for this purpose, but rejected,
> in part because it was believed at the time to bring a burden of
> overhead and complexity with it; we (the MIDAS XML group) opted for this
> customised approach because it allowed us to capture the required
> spatial content without becoming overly complex. Of equal importance, it
> was specifically tailored to suit both the granular nature of HER
> spatial data, and the the relatively basic level of XML -- and
> particularly spatial XML -- acumen in HERs and their parent authorities.
> 
> To be fair, I would not go so far as to say that the approach we have
> taken is, as you suggest, proprietary: there is nothing in the schema
> that cannot be transformed into GML, and we also endorse the use of
> OGC-supported WKT for representing geometry (largely because this format
> can be understood by spatial databases without requiring
> transformation); lastly, the representation itself was influenced in
> part by various components of the the OGC-supported WMS protocol.
> 
> Saying that, however, I am keen to stress above all else that I am all
> for improving MIDAS XML wherever possible, and especially exploring
> alternatives that simultaneously capture the required data, support
> extant standards, and make it easier for HERs to use.  If this is what
> will make the exchange of heritage information more straightforward and
> less of a headache for HER officers, then it should certainly be pursued.
> 
> Regards,
> 
> Tyler
> 
> ---
> Dr Tyler Bell
> Director
> Oxford ArchDigital Ltd.
> 
> 
> 
> 
> Ian Painter wrote:
> 
>>Hi Trevor,
>>
>>Geography Markup Language (GML) is a standard created by the Open
>>Geospatial Consortium (OGC) http://www.opengeospatial.org to allow the
>>exchange of geographical information between computer systems.
>>
>>To start at the beginning, GML is an extension of XML (eXtensible Markup
>>Language). XML is a standard defined by the W3C (World Wide Web
>>Consortium). XML defines some basic constructs for forming data formats
>>such as the idea of a data element, basic types like strings, numbers
>>and dates etc. Most importantly, XML defines a standard way of adding
>>extensions to XML to make a more specific format. This mechanism for
>>defining formats is called XML Schema.
>>
>>The OGC have used XML Schema to add some geographical concepts to XML.
>>So, for example, GML defines the concept of a geographical feature,
>>line, point and area geometry and so on. These extensions are specified
>>in two XML Schema files, features.xsd and geometry.xsd (XML Schema files
>>usually have the ".xsd" file name extension).
>>
>>However, these are still abstract definitions, and so GML needs to be
>>extended further to express the elements relevant to a particular
>>dataset. For example, whilst GML says there is such thing as a feature a
>>particular format might extend this to say that there is a kind of
>>feature called "Road". GML says that features can have geometry
>>attributes that are lines, points or areas. The particular format might
>>specify that a "Road" has a geometry attribute that is a line. A
>>particular format will be specified in one or more XML Schema files
>>(".xsd" files). The XML Schema that defines a particular format is known
>>as the application schema. The application schema files should be
>>supplied by your data provider along with GML data itself.
>>
>>GML is mature and stable ISO adopted standard (ISO 19136) currently in
>>its 3 major iteration, you can find the full (and very detailed) spec
>>along with its associated XML Schemas here:
>>
>>http://opengis.net/gml/
>>
>>The best resource is simple 6 stage online introduction here:
>>
>>http://gislounge.com/ucon/ucgmlintro.shtml
>>
>>Hope this helps
>>
>>Ian
>>
>>
>>
>>-----Original Message-----
>>From: The Forum for Information Standards in Heritage (FISH)
>>[mailto:[log in to unmask]] On Behalf Of REYNOLDS, Trevor
>>Sent: 22 November 2005 10:06
>>To: [log in to unmask]
>>Subject: Re: [FISH] Feedback on the MIDAS schema
>>
>>Ian
>>
>>Could you give me a quick explanation of GML - I've never heard of it
>>before.
>>
>>Trevor Reynolds
>>Collections Registrar, English Heritage, Room 530, 23 Savile Row, London
>>W1S 2ET, United Kingdom
>>Tel: +44 (0) 20 7973 3482  Fax: +44 (0) 20 7973 3209
>>
>>
>>
>>>-----Original Message-----
>>>From: The Forum for Information Standards in Heritage (FISH)
>>>[mailto:[log in to unmask]] On Behalf Of Ian Painter
>>>Sent: 21 November 2005 17:17
>>>To: [log in to unmask]
>>>Subject: [FISH] Feedback on the MIDAS schema
>>>
>>>Hi All,
>>>
>>>We've had a number of queries from our customers and partners
>>
>>regarding
>>
>>
>>>our ability to support the MIDAS schema.  Firstly, let me give you a
>>>little background. I'm from a company called Snowflake Software and we
>>
>>
>>>specialise in schema aware XML / GML loading and publishing tools. We
>>>are a member of the Open Geospatial Consortium and play an active part
>>
>>
>>>in helping develop and promote GML. The MIDAS schemas look great and
>>
>>its
>>
>>
>>>great to see XML being published in the heritage field.
>>>=====================