RDF, Big Data and The Semantic Web

I’ve been meaning to write this post for a little while, but things have been busy. So, with this afternoon free I figured I’d write it now.

I’ve spent the last 7 years working intensively with data. Mostly not with RDBMSs, but with different Big Data and Linked Data tools. Over the past year things have changed enormously.

The Semantic Web

A lot has been talked about the Semantic Web for a long time now. In fact, I often advise people to search for Linked Data rather than Semantic Web as the usefulness of the results in a practical context is vast. The semantic web has been a rather unfortunately academic endeavour that has been very hard for many developers to get into. In contrast, Linked Data has seen explosive growth over the past five years. It hasn’t gone mainstream though.

What does show signs of going mainstream is the schema.org initiative. This creates a positive feedback loop between sites putting structured data into their pages and search engines giving those sites more and better leads as a result.

Much has been said about Microdata killing RDF blah, blah but that’s not important. What is important is that publishing machine-understandable data on the web is going mainstream.

As an aside, as Microdata extends to solve the problems it currently has (global identifiers and meaningful links) it becomes just another way to write down the RDF model anyway. RDF is an abstract model, not a data format, and at the moment Microdata is a simplified subset of that model.

Big Data and NoSQL

In the meantime another data meme has also grown enormously. In fact, it has dwarfed Linked Data in the attention it has captured. That trend is Big Data and NoSQL.

In Planning for Big Data, Edd talks about the three Vs:

To clarify matters, the three Vs of volume, velocity and variety are commonly used to characterize different aspects of big data. They’re a helpful lens through which to view and understand the nature of the data and the software plat- forms available to exploit them. Most probably you will contend with each of the Vs to one degree or another.

Most Big Data projects are really focussed on volume. They have large quantities, terabytes or petabytes, of uniform data. Often this data is very simple in structure, such as tweets. Fewer projects are focussed on velocity, being able to handle data coming in quickly and even fewer on variety, having unknown or widely varied data.

You can see how the Hadoop toolset is tuned to this and also how the NoSQL communities focus mostly on denormalisation of data. This is a good way to focus resources if you have large volumes of relatively simple, highly uniform data and a specific use-case or queries.

Apart from Neo4J, which is the odd-one-out in the Big Data community this is the approach.


So, while we wait for the semantic web to evolve, what is RDF good for today?

That third V of the Big Data puzzle is where I’ve been helping people use graphs of data (and that’s what RDF is, a graph model). Graphs are great where you have a variety of data that you want to link up. Especially if you want to extend the data often and if you want to extend the data programmatically — i.e. you don’t want to commit to a complete, constraining schema up-front.

The other aspect of that variety in data that graphs help with is querying. As Jem Rayfield (BBC News & Sport) explains, using a graph makes the model simpler to develop and query.

Graph data models can reach higher levels of variety in the data before they become unwieldy. This allows more data to be mixed and queried together. Mixing in more data adds more context and more context adds allows for more insight. Insight is what we’re ultimately trying to get at with any data analysis. That’s why the intelligence communities have been using graphs for many years now.

What we’re seeing now, with the combination of Big Data and graph technologies, is the ability to add value inside the enterprise. Graphs are useful for data analysis even if you don’t intend to publish the data on the semantic web. Maybe even especially then.

Microsoft, Oracle and IBM are all playing in the Big Data space and have been for some time. What’s less well-known and less ready for mainstream is that they all have projects in the graph database space: DB2 NoSQL Graph StoreOracle Database Semantic TechnologiesConnected Services Framework 3.0.

Behind the scenes, in the enterprise, is probably the biggest space where graphs will be adding real value over the next few years; solving the variety problem in Big Data.

What next?

I’m leaving Talis.

For the past seven years I have had the great fortune to learn a huge amount from awesome people. That has put me in the position of having some great conversations about what I’ll be doing next; and those conversations are exciting. More on that in a later post. First, how can someone be happy to be leaving a great company?

Back in late 2004 I joined a small library software vendor with some interesting challenges, Talis. Since then we have become one of the best known Linked Data and Semantic Web brands in the world. On that journey I have learnt so much. I’ve learnt everything from an obscure late 1960s data format (MARC) to Big Data conversions using Hadoop. The technology has been the least of it though.

I’ve been rewarded with the opportunity to hear some of the smartest people in the world speak in some amazing places. I’ve pair-programmed with Ian Davis and had breakfast with Tim Berners-Lee; I’ve seen the Rockies in Banff and walked the Great Wall of China. As a result of our brand and the work we’ve done I’ve been invited to help write the first license for open data; train government departments on how to publish their data and talk about dinosaurs with Tom Scott at the BBC.

Talis has always been about the people. People in Talis (Talisians); people outside we’ve worked with and bounced ideas off; customers who have allowed us to help with exciting projects. I have made some great friends and been taught some humbling lessons.

Amongst the sharpest highlights has been an enormously rewarding day job. At the start re-imagining Talis Base and then Talis Prism; seeding an education-focussed business and recently building an expert, international consultancy.

I joined Talis expecting to stay for a few years and found the journey so rewarding it has kept me for so much longer. It’s now time for my journey and Talis to diverge as I think about doing something different.

I still have a couple of consulting engagements to finalise, so if you’re one of those then please don’t panic; we’ll be talking soon.

There is no “metadata”

For a while I’ve been avoiding using the term metadata for a few reasons. I’ve had a few conversations with people about why and so I thought I’d jot the thoughts down here.

First of all, the main reason I stopped using the term is because it means too many different things. Wikipedia recognises metadata as an ambiguous term

The term metadata is an ambiguous term which is used for two fundamentally different concepts (types). Although the expression “data about data” is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at design time the application contains no data. In this case the correct description would be “data about the containers of data”. Descriptive metadata, on the other hand, is about individual instances of application data, the data content. In this case, a useful description (resulting in a disambiguating neologism) would be “data about data content” or “content about content” thus metacontent. Descriptive, Guide and the National Information Standards Organization concept of administrative metadata are all subtypes of metacontent.

and even within the world of descriptive metadata the term is used in many different ways.

I have always found a better, more accurate, complete and consistent term. Such as catalogueprovenanceauditlicensing and so on. I haven’t come across a situation yet where a more specific term hasn’t helped everyone understand the data better.

Data is just descriptions of things and if you say what aspects of a thing you are describing then everyone gets a better sense of what they might do with that. Once we realise that data is just descriptions of things, written in a consistent form to allow for analysis, we can see the next couple of reasons to stop using metadata.

Meta is a relative term. Ralph Swick of W3C is quoted as saying

What’s metadata to you, is someone else’s fundamental data.

That is to say, wether you consider something meta or not depends totally on your context and the problem you’re trying to solve. Often several people in the room will consider this differently.

If we combine that thought with the more specific naming of our data then we get the ability to think about descriptions of descriptions of descriptions. Which brings me on to something else I observe. By thinking in terms of data and metadata we talk, and think, in a vocabulary limited to two layers. Working with Big Data and Graphs I’ve learnt that’s not enough.

Taking the example of data about TV programming from todays RedBee post we could say:

  1. The Mentalist is a TV Programme
  2. The Mentalist is licensed to Channel 5 for broadcast in the UK
  3. The Mentalist will be shown at 21.00 on Thursday 12 April 2012

Statement 2 in that list is licensing data, statement 3 is schedule data. This all comes under the heading of descriptive metadata. Now, RedBee are a commercial organisation who put constraints on the use of their data. So we also need to be able to say things like

  • Statements 1, 2 and 3 are licensed to BBC for competitor analysis

This statement is also licensing data, about the metadata… So what is it? Descriptive metametadata?

Data about data is not a special case. Data is just descriptions of things and remains so wether the things being described are people, places, TV programmes or other data.

That’s why I try to replace the term metadata with something more useful whenever I can.