13 September 2014

A schemaless computer database in 1965

To enable flexible metadata aggregation, among other things.

figure 3

I've been reading up on America's post-war attempt to keep up the accelerated pace of R&D that began during World War II. This effort led to an infrastructure that made accomplishments such as the moon landing and the Internet possible; it also led to some very dry literature, and I'm mostly interested in what new metadata-related techniques were developed to track and share the products of the research as they led to development.

One dry bit of literature is the proceedings of the 1965 Toward a National Information System: Second Annual National Colloquium On Information Retrieval. The conference was sponsored by the American Documentation Institute, who had a big role in the post-war information sharing work, as well as the University of Pennsylvania's Moore School of Electrical Engineering (where Eckert and Mauchly built ENIAC and its successor EDVAC) and some ACM chapters.

In a chapter on how the North American Aviation company (now part of Boeing) revamped their practices for sharing information among divisions, I came across this description of some very flexible metadata storage:

All bibliographic information contained in both the corporate and divisional Electronic Data Processing (EDP) subsystems is retained permanently on magnetic tape in the form of variable length records containing variable length fields. Each field, with the exception of sort keys, consists of three adjacent field parts: field character count, field identification, and field text (see Figure 3). There are several advantages to this format: it is extremely compact, thereby reducing computer read-write time; it provides for definition and consequent addition of new types of fields of bibliographic information without reformatting extant files; and its flexibility allows conversion of files from other indexing abstracting services.

I especially like that "it provides for definition and consequent addition of new types of fields of bibliographic information without reformatting extant files." This reminds me of one slide in my presentation last month at the Semantic Technology and Business / NoSQL Now! conferences last month, where my talk was on a track shared by both conferences, about how a key advantage of schemaless NoSQL databases is the ability to add a new value for a new property to a data set with no need for the schema evolution steps that can be so painful in a relational database.

Moore's law has led to less of a reliance on arranging data in tables to allow the efficient retrieval of that data. The various NoSQL options have explored new ways to do this, and it was great to see that one aerospace company was doing it 49 years ago. Of course, retrieving data from magnetic tape is less efficient than modern alternatives, but it was a big step past the use of piles of punched cards, and pretty modern for its time, as you can see from the tape spools on the picture of EDVAC's gleaming successor below. I thought it was cool to see that, although tabular representation of data long predates relational databases (hierarchical and network databases also stored sets of entities as tables, but with much less flexibility) that someone had implemented such a flexible model so long ago, especially to represent metadata, with a use case that we often see now with RDF: to allow "conversion of files from other indexing abstracting services"—in other words, to accomodate the aggregation of metadata from other sources that may not have structured their data the same way that yours is structured.

Univac 9400

Univac photo by H. Müller CC-BY-SA-2.5, via Wikimedia Commons

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24 August 2014

Exploring a SPARQL endpoint

In this case, semanticweb.org.

graph of ISWC SPARQL papers

In the second edition of my book Learning SPARQL, a new chapter titled "A SPARQL Cookbook" includes a section called "Exploring the Data," which features useful queries for looking around a dataset that you know little or nothing about. I was recently wondering about the data available at the SPARQL endpoint http://data.semanticweb.org/sparql, so to explore it I put several of the queries from this section of the book to work.

An important lesson here is how easy SPARQL and RDF make it to explore a dataset that you know nothing about. If you don't know about the properties used, or whether any schema or schemas were used and how much they was used, you can just query for this information. Most hypertext links below will execute the queries they describe using semanticweb.org's SNORQL interface.

I started with what is generally my favorite query, listing which predicates are used in the data, because that's the quickest way to get a flavor for what kind of data is available. Several of the predicates that got listed immediately told me some interesting things:

  • rdfs:subClassOf shows me that there's probably some structure worth exploring.

  • dcterms:subject (and dc:subject) shows that things have probably been tagged with keywords.

  • ical properties such as dtstart shows that events are recorded.

  • FOAF properties show that there is probably information about people.

  • dcterms:title, swrc:booktitle, dc:title, src:title, and swrc:subtitle show me that works are covered.

An RDF dataset may or may not have explicit structure, and the use of rdfs:subClassOf in this data showed me that there was, so my next query asked what classes were subclasses of what classes so that I could get an overview of how much structure the dataset included. The result showed me that the ontology seemed to be mostly in the swc namespace, which turns out to be the semanticweb.com conference ontology. The site does include nice documentation for this ontology.

The use of the FOAF vocabulary showed me that there are probably people described, but if the properties foaf:name, foaf:lastName, foaf:familyName, foaf:family_name, and foaf:surname are all in there, which should I try first? A quick ego search showed foaf:family_name being used. It also showed that the URI used to represent me is http://data.semanticweb.org/person/bob-ducharme, and because they've published this data as linked data, sending a browser to that URL showed that it described me as a member of the 2010 ISWC program committee.

It also showed me to be a proud instance of the foaf:Person class, so I did a query to find out how many persons there were in all: 10,982.

Given the domain of the ontology and the reason that I was listed, I guessed that it was all about ISWC conferences, so I listed the dc:title values to see what would show up. The query took long enough that I added a LIMIT keyword to create a politer version of that query. Looking at the complete data for one work showed all kinds of interesting information, including an swrc:year value to indicate the year of this paper's conference. A list of all year values showed a range from 2001 right up to 2014, so it's nice to see that they're keeping the data up to date.

Next, I listed all papers that mention "SPARQL" in their title, with their years. After listing the number of papers with SPARQL in their title each year, I used sgvizler (which I described here last September) to create the chart of these figures shown above.

The use of dcterms:subject and dc:subject was interesting because these add some pretty classic metadata for navigating content. Listing triples that used either, I included LIMIT 100 to be polite to the server in case these properties were used a lot. They are. Doing this with dc:subject shows subjects such as "ontology alignment" and "controlled natural language" assigned to articles. Doing it with dcterms:subject showed it used more the way I might use rdf:type, indicating that something is an instance of a particular class: for example, swc:Chair and swc:Delegate each have dcterms:subject values of http://dbpedia.org/resource/Role.

My interest in taxonomies (spurred by my work with TopQuadrant's TopBraid EVN) led me to look harder at the dc:subject values. They're string values, and not instances of something like skos:Concept, so they have no hierarchical relationship or other metadata themselves. I'm guessing that this is because key phrases assigned to conference papers are more of a folksonomy, in which people can make up their own key phrases as they wish. Either some people must have been aware of other key phrases in use or some were added automatically, because, while counting how many different ones there were came up with 3,594, a query to see which were the most popular showed that "Corpus (creation, annotation, etc.)" was far and away the most used, with 506 papers having that subject.

I could go on. Call me a SPARQL geek, but I really enjoy looking around a data set like this, especially when (as the presence of the papers for ISWC 2014 shows) the data is kept up to date. For people interested in any aspect of semantic web technology, the ability to look around this particular dataset and count up which data falls into which patterns is a great resource.

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20 July 2014

When did linking begin?

Pointing somewhere with a dereferenceable address, in the twelfth (or maybe fifth) century.

University of Bologna woodcut

As I have once before, I'm republishing an entry from an O'Reilly blog I had from 2003 to 2005 on topics related to linking. I've been reading up on early concepts of metadata lately—I particularly recommend Ann Blair's Too Much to Know: Managing Scholarly Information before the Modern Age—and have recently found another interesting reference to the "Regulae Iuris" book mentioned below. When I wrote this, I was more interested in hypertext issues, and if I was going to change anything to update this piece, I would change the word "traverse" to "dereference," but all the points are still meaningful.

Works about linking often claim that it's been around for thousands of years, and then they give examples that are no more than a few centuries old. I can only find one reference to something more than a thousand years old that qualifies as a link: Peter Stein's 1966 work "Regulae Iuris: from Juristic Rules to Legal Maxims" describes some late fifth-century lecture notes on a commentary by the legal scholar Ulpian. The notes mention that confirmation of a particular point can be found in the Regulae ("Rules") of the third-century Roman jurist (and student of Ulpian) Modestinus, "seventeen regulae from the end, in the regula beginning 'Dotis'...". The citation's explicit identification of the point in the cited work where the material could be found makes it the earliest link that I know of.

Other than Stein's tantalizing example, all of my research points to the 12th century as the beginning of linking. In a 1938 work on the medieval scholars of Bologna, Italy, who studied what remained of ancient Roman law, Hermann Kantorowicz wrote that in "the eleventh century...titles of law books are cited without indicating the passage, books of the Code are numbered, and the name of the law book is considered a sufficient reference." He uses this to build his argument that that a particular work described in his essay is from the eleventh century and not the twelfth, as other scholars had argued. Apparently, it was common knowledge in Kantoriwicz's field that twelfth century Bolognese scholars would reference a written law using the name of the law book, the rubric heading, and the first few words of the law itself. (Referencing of particular chapters and sections by their first few words was common at the time; the use of chapter, section, and page numbers didn't begin until the following century.)

Italian legal scholars trying to organize and make sense of the massive amounts of accumulated Roman law contributed a great deal to the mechanics of the cross-referencing that provide many of the earliest examples of linking. The medievalist husband and wife team Richard and Mary Rouse also found some in their research into evolving scholarship techniques in the great universities of England and France (that is, Oxford, Cambridge, and the Sorbonne) and they described Gilbert of Poitiers's innovative twelfth-century mechanism for addressing specific parts of his work on the psalms: he added a selection of Greek letters and other symbols down the side of each page to identify concepts such as the Penitential Psalms or the Passion and Resurrection. If you found the symbol for the Passion and Resurrection in the margin of Psalm 2 with a little 8 next to it (actually, a little "viii"—they weren't using Arabic numerals quite yet), it would tell you that the next discussion of this concept appeared in Psalm 8. Once you found the same symbol on one of the eighth psalm's pages, you might find a little "xii" with it to show that the next discussion of the same concept was in Psalm 12. This addressing system made it possible for someone preparing a sermon on the Passion and Resurrection to easily find the relevant material in the Psalms. (In fact, aids to sermon preparation was one of the main forces in the development of new research tools, as clergymen were encouraged to go out and compete with the burgeoning heretic movements for the hearts and minds of the people.)

The use of information addressing systems really got rolling in the thirteenth-century English and French universities, as scholarly monks developed concordances, subject indexes, and page numbers for both Christian religious works and the classic ancient Greek works that they learned about from their contact with the Arabic world. In fact, this is where Arabic numbers start to appear in Europe; page numbering was one of the early drivers for its adoption.

Quoting of one work by another was certainly around long before the twelfth century, but if an author doesn't identify an address for his source, his reference can't be traversed, so it's not really a link. Before the twelfth century, religious works had a long tradition of quoting and discussing other works, but in many traditions (for example, Islam, Theravada Buddhism, and Vedic Hinduism) memorization of complete religious works was so common that telling someone where to look within a work was unnecessary. If one Muslim scholar said to another "In the words of the Prophet..." he didn't need to name the sura of the Qur'an that the quoted words came from; he could assume that his listener already knew. Describing such allusions as "links" adds heft to claims that linking is thousands of years old, but a link that doesn't provide an address for its destination can't be traversed, and a link that can't be traversed isn't much of a link. And, such claims diminish the tremendous achievements of the 12th-century scholars who developed new techniques to navigate the accumulating amounts of recorded information they were studying.

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