Jeni's Musings

This is the third in a series of posts about using the Talis Platform as a back end for serving linked data. In the first part, I showed how to add data to a store. In the second post, I showed how to use some PHP scripts to publish the data as Linked Data, at the URLs you use as your identifiers.

In this post, I’m going to begin the process of exposing the data in a way that makes it easy to locate and reuse. One of the biggest lessons I learned after the initial publication of the London Gazette data as RDFa is that the publication of data and metadata about individual items is not enough. To make the data usable, you have to make it discoverable. To make it discoverable there must be an entry point from which you can locate the data. One kind of easy entry point is a list.

In the case of the data about London Boroughs that I’ve been using, there aren’t currently any links to the data, so there is no way to discover it aside from me telling you the URI template (http://www.jenitennison.com/data/id/london-borough/{name}, where name is hyphenated and in lowercase) and you knowing the name of a London Borough that you want to look up. Discovery via a URI template that I told you relies on out-of-band information, and contradicts the RESTful tenet of “hypertext as the engine of application state”.

Instead, I need to offer an entry point from which you can follow links (or fill in forms) to discover information about the various London Boroughs. Since I’m dealing with a small set of information here, I’m going to do this in the straight-forward way of having http://www.jenitennison.com/data/london-borough contain a brief description of each of the known London Boroughs, including (obviously) a link to the URI for the London Borough, from which you can get more information.

In my last post, I showed how to add data to a Talis store. In this post, I’m going to show how you can use the Talis Platform as a back end for a Linked Data view on the RDF you added to it.

As you’ll see, the great thing about this method is that it only takes a couple of PHP files and an .htaccess file on a server. Assuming that you’ve got a web server that supports PHP, it’s an approach you can use without installing anything. The code I’ve written is pretty generic and should be widely applicable; feel free to reuse and adapt it.

I was at OpenTech a couple of weekends ago, and heard a lot of great talks. I particularly enjoyed the one by Simon Willison in which he talked about the Guardian Data Blog. Essentially, the data collected by the journalists at the Guardian, that form the basis of their pretty visualisations and so forth, gets published in Google Spreadsheets.

Looking through the data blog today, I saw that the Greater London Authority have similarly released their data using Google Spreadsheets.

Now Google Spreadsheets are just fine – they’re easy for end-users to use and it’s not hard for data nerds to extract data from them. They have real advantages for publishing because they are quick and easy to set up.

But take a look through the page listing the tables of data and you can see that many of them are about the same areas. The Guardian Data Blog have actually created a new spreadsheet that pulls together that information. Even with the aggregated data, in Google Spreadsheets there’s no way to address the data held in each table about Sutton (say).

Now, a few months ago, Talis announced the Talis Connected Commons, which enables anyone to publish public domain data using the Talis Platform for free. It turns out that it’s really easy to publish addressable data using the Talis Platform as a host.

There’s a big push within the UK government right now, helped along by the appointment of Tim Berners-Lee, to publish their data using Linked Data principles.

One of the challenges is how to publish Linked Data in a world that sometimes, even frequently, changes. Cool URIs don’t change, but departmental domain names do, as departments are split and merged and rebranded. So the URIs that are minted for things like schools and roads need to be detached from the departments that have responsibility for them, neutralised into general domains such as education.data.gov.uk and transport.data.gov.uk.

But that’s the least of the problems. Because schools and roads themselves don’t remain static either. They are split and merged and rebranded. They are resources that change over time. What should their URIs look like?

Registration has just opened for this year’s XML Summer School, held in Oxford on 20-25th September. I’m teaching a couple of sessions and helping with a workshop on the “XSLT, XSL-FO and XQuery” track along with Bob DuCharme, Michael Kay and Priscilla Walmsley. It’s one of my favourite events, for three reasons:

• I get to listen to experts talk about particular technologies in depth. The sessions are particularly good because they’re provided by people who don’t just spend all their time training, but actually practice what they’re talking about, and therefore positively relish the kinds of discussions that normal trainers might shy away from.
• I get to meet a whole bunch of people who are using XML in different areas: publishing, healthcare, government, you name it. In that way it’s like a conference: many of the most useful conversations happen during the breaks or at the bar.
• I get to go punting, visit Oxford’s best pubs and dress up for a formal dinner – more social engagements in a single week than I usually have in a year!

I know a lot of beginners go to the XML Summer School for the introduction course, but to me the real value is for people who are actually using XML on a day to day basis and want to keep on top of the latest tools and technologies that will actually help them do their jobs. I learn something new every year.

Anyway, I wanted to blog about it because there’s a discount on registration up until 30th June. Grab ‘em while you can!