It's been quite a while since my last post. This has mostly been due to spending a large amount of time playing with some Topic Map (the Ontopia Omnigator) and OWL (Protege) software. Both of these are excellent applications and I was especially impressed by the ability of OWL to form advanced object relationships.
However, at the end of all this research, I think that neither Topic Maps nor OWL are suitable for my purposes; yes, both can perform complex classifications and describe advanced relationships between classes but, for my purposes of creating a heterogeneous database, I only require simple classifications and relationships. Therefore using either of these technologies would probably be like taking the proverbial hammer to a nut. For me, a stronger argument against using these technologies is that, at this moment in time, neither is freely available for C# - the language that I'd like to work with.
So my requirements are a technology that can describe simple classifications and relationships and that is freely available in C#. The one application that seems to match these requirements is Joshua Tauberer's SemWeb - an RDF library for C#. The RDF and RDFS support provided by this package can perform categorisation and describe the relationships between objects to a level suitable for my requirements. An added bonus is that this library is still under active development - version 1.0 was only released on the 10th June 2007 (unlike the other C# RDF library Drive - the web page of which had actually expired the last time I looked).
This doesn't mean to say that SemWeb is perfect - like most things I've encountered on this journey, using SemWeb is not as straightforward as it could be. The main reason for this is that SemWeb has been developed on Mono, as opposed to Microsoft's Visual Studio that I want to use. As a result of this the supplied Visual Studio solutions are incomplete (I needed to refer to the makefiles to create the required projects) and the package currently doesn't support SQL Server, the Express version of which I'd been using for some other areas of this project (such as user administration). I've therefore now switched databases to use MySQL and am now struggling to add and retrieve some RDF data from this. I'll give more details of this struggle in the next post.
Showing posts with label topic maps. Show all posts
Showing posts with label topic maps. Show all posts
Monday, 2 July 2007
Wednesday, 16 May 2007
RDF - An alternative to Topic Maps?
In my last post I described how Topic Maps appeared to be a possible mechanism for creating a flexible database, capable of storing a range of different, and possibly unrelated, items - a heterogeneous database. However, as I also mentioned previously, a couple of things worried me about Topic Maps; namely that work in the area seems to have gone a bit quiet in the last couple of years and, secondly, that there appears to be quite a large European bias to the companies and institutions working in the field - not that this is a bad thing, but what are everyone else up to?
These two things were playing on my mind, so rather than rushing headlong into Topic Maps, I decided to take a step back and spend a bit more time investigating other possible solutions. This search revealed that there is another possible solution to the problem - RDF - the Resource Description Framework (I'd already suggested in my last post that this could be a possibility). Indeed RDF and Topic Maps appear to cover very similar ground and, from an initial study of the available information, it's hard to decide between the two. It may be that subtle differences exist between the two technologies but my initial impression is that they are pretty much going head-to-head against each other – another VHS versus Betamax, but with probably slightly less interest from the general public.
So what are the actual differences between RDF and Topic Maps and which technology is the most suitable for my purposes? As with Topic Maps, the documentation for RDF is rather sparse and also seems to mostly be a couple of years old - the only book I could find that described both subjects was The Explorer's Guide to the Semantic Web, published in 2004. While this provided a good overview of both technologies, it didn't really cover them at a low enough level for my needs and, by the end, I was still left uncertain of the differences in the two. In addition, RDF has other related technologies - namely RDFS (RDF Schema) and OWL (Web Ontology Language - which surely should be called WOL, although this would have reduced the oportunities to publish books with bird covers) and I felt that these weren't covered in enough detail. The only thing for it was to dig a bit deeper into each subject.
RDF, RDFS and OWL
The definitive (and about the only) text on RDF is Shelley Power's Practical RDF. This book did give low level descriptions of RDF, RDFS and OWL and I'd definitely recommend it for anyone interested in RDF. My only criticism would be that the chapters describing RDF tools are now a bit out of date (the book was published in 2003) and I found quite a few typos and mistakes in the RDF examples - a new edition of the book is surely required. However, by the end, I felt that I'd gained enough knowledge to pursue RDF a bit further.
I think I now understand how RDF, RDFS and OWL fit together. My interpretation is that RDF is a mechanism that can describe simple relationships (subject-predicate-object expressions, known as triples e.g. apples have the colour green). RDF can be serialized using RDF\XML (i.e. an XML based language can be used to describe the RDF relationships). RDF Schema can then be used, in much the same way as XML Schema (XSD) are used with XML, to describe the contents and structure of the RDF, allowing relationships to be created. OWL is effectively built on top of RDFS, extending it to allow the generation of complex class and sub-class relationships.
I'm still not sure about the differences in Topic Maps and RDF (the RDF book didn't cover Topic Maps), so I think the only thing for it is to play with the two technologies. I'll let you know how it goes in the next post.
These two things were playing on my mind, so rather than rushing headlong into Topic Maps, I decided to take a step back and spend a bit more time investigating other possible solutions. This search revealed that there is another possible solution to the problem - RDF - the Resource Description Framework (I'd already suggested in my last post that this could be a possibility). Indeed RDF and Topic Maps appear to cover very similar ground and, from an initial study of the available information, it's hard to decide between the two. It may be that subtle differences exist between the two technologies but my initial impression is that they are pretty much going head-to-head against each other – another VHS versus Betamax, but with probably slightly less interest from the general public.
So what are the actual differences between RDF and Topic Maps and which technology is the most suitable for my purposes? As with Topic Maps, the documentation for RDF is rather sparse and also seems to mostly be a couple of years old - the only book I could find that described both subjects was The Explorer's Guide to the Semantic Web, published in 2004. While this provided a good overview of both technologies, it didn't really cover them at a low enough level for my needs and, by the end, I was still left uncertain of the differences in the two. In addition, RDF has other related technologies - namely RDFS (RDF Schema) and OWL (Web Ontology Language - which surely should be called WOL, although this would have reduced the oportunities to publish books with bird covers) and I felt that these weren't covered in enough detail. The only thing for it was to dig a bit deeper into each subject.
RDF, RDFS and OWL
The definitive (and about the only) text on RDF is Shelley Power's Practical RDF. This book did give low level descriptions of RDF, RDFS and OWL and I'd definitely recommend it for anyone interested in RDF. My only criticism would be that the chapters describing RDF tools are now a bit out of date (the book was published in 2003) and I found quite a few typos and mistakes in the RDF examples - a new edition of the book is surely required. However, by the end, I felt that I'd gained enough knowledge to pursue RDF a bit further.
I think I now understand how RDF, RDFS and OWL fit together. My interpretation is that RDF is a mechanism that can describe simple relationships (subject-predicate-object expressions, known as triples e.g. apples have the colour green). RDF can be serialized using RDF\XML (i.e. an XML based language can be used to describe the RDF relationships). RDF Schema can then be used, in much the same way as XML Schema (XSD) are used with XML, to describe the contents and structure of the RDF, allowing relationships to be created. OWL is effectively built on top of RDFS, extending it to allow the generation of complex class and sub-class relationships.
I'm still not sure about the differences in Topic Maps and RDF (the RDF book didn't cover Topic Maps), so I think the only thing for it is to play with the two technologies. I'll let you know how it goes in the next post.
Sunday, 15 April 2007
Information Architecture and Topic Maps
Umm... things aren't as straightforward as I'd initially imagined. On investigating what's required for heterogeneous databases I've discovered that there's a whole world of stuff out there that I know little or nothing about: facets, synonym rings, and controlled vocabularies to name but a few. In fact this world has a name: Information Architecture and even its own bible, the legendary Polar Bear Book. Hidden amongst all this lies the mysterious field of Topic Maps. From my initial skimming of the available resources and documentation on the subject, it sounds as if these may be exactly what I’m after.
I describe Topic Maps as being mysterious for two reasons: Firstly, after an initial flurry of activity in the area at the turn of the century, it appears as if things have now gone a bit quiet. The Topic Maps standard, ISO/IEC 13250 and the related XML Topic Maps (XTM), were last published in 2002 and 2001 respectively. The only book I could find on the subject, XML Topic Maps, was also published in 2002. Additionally, many of the main published links on the subject no longer exist. The second reason that Topic Maps are a bit mysterious is the fact that the vast majority of the research, and companies working in the area, seems to be concentrated in Europe – America seems to be ignoring their existence; either Europe is at the cutting edge of this technology, or something equivalent must exist that’s being used in America and I haven’t discovered it yet! (RDF and OWL perhaps?).
Topic Maps – The Basics
In Topic Maps nearly everything is represented as a standalone entity - a topic, and relationships can be created between these topics. For example, if we wished to describe a book, we could create separate topics for the name of the author, the title of the book, the publisher of the book, etc. and other topics to describe the relationships between these topics – for example, that this book was written by the author. This makes it possible to create relationships for practically anything and therefore it’s also possible to create a relational database that can be used to represent anything, which is exactly what I’m after. In addition, new topics and relationships can be added as more information is known about a subject.
In the next post I’ll hopefully describe how a topic map database can be created and how a range of different subjects can be stored. For anyone who can’t wait till then, some useful Topic Map information can be found at the following links:
"Metadata? Thesauri? Taxonomies? Topic Maps!" http://www.ontopia.net/topicmaps/materials/tm-vs-thesauri.html
Topic Maps and Relational Databases
http://www.xml.com/pub/a/2003/03/05/tmrdb.html
I describe Topic Maps as being mysterious for two reasons: Firstly, after an initial flurry of activity in the area at the turn of the century, it appears as if things have now gone a bit quiet. The Topic Maps standard, ISO/IEC 13250 and the related XML Topic Maps (XTM), were last published in 2002 and 2001 respectively. The only book I could find on the subject, XML Topic Maps, was also published in 2002. Additionally, many of the main published links on the subject no longer exist. The second reason that Topic Maps are a bit mysterious is the fact that the vast majority of the research, and companies working in the area, seems to be concentrated in Europe – America seems to be ignoring their existence; either Europe is at the cutting edge of this technology, or something equivalent must exist that’s being used in America and I haven’t discovered it yet! (RDF and OWL perhaps?).
Topic Maps – The Basics
In Topic Maps nearly everything is represented as a standalone entity - a topic, and relationships can be created between these topics. For example, if we wished to describe a book, we could create separate topics for the name of the author, the title of the book, the publisher of the book, etc. and other topics to describe the relationships between these topics – for example, that this book was written by the author. This makes it possible to create relationships for practically anything and therefore it’s also possible to create a relational database that can be used to represent anything, which is exactly what I’m after. In addition, new topics and relationships can be added as more information is known about a subject.
In the next post I’ll hopefully describe how a topic map database can be created and how a range of different subjects can be stored. For anyone who can’t wait till then, some useful Topic Map information can be found at the following links:
"Metadata? Thesauri? Taxonomies? Topic Maps!" http://www.ontopia.net/topicmaps/materials/tm-vs-thesauri.html
Topic Maps and Relational Databases
http://www.xml.com/pub/a/2003/03/05/tmrdb.html
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