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Archive for November, 2014

Empirical analysis of UK legislation started this weekend

November 23rd, 2014 No comments

Yesterday I was one of a dozen or so people at a hackathon hosted by the Ministry of Justice. I’m sure that the organizers would have liked a lot more people attending, but the McDonald’s hackathon across town was a bigger draw for most of the hackers I know.

The dataset was all UK legislation back to 1988, and a less complete set going back to 1267, in html and various flavors of xml; in all 20G of compressed files, with the compressed html files occupying 7G on my machine. As of this weekend the files are available online.

There were about half a dozen domain experts, in various aspects of the creation of UK legislation, present and they suggested lots of interesting questions that we (i.e., the attendees who could code) might like to try to answer.

I was surprised at the simplicity of some questions, e.g., volume (e.g., word count) of legislation over time and branch of government. The reason these question had not been answered before is that the data had not been available; empirical analysis of UK legislation started this weekend.

The most interesting question I heard involved the relative volume of primary and secondary legislation. Primary legislation is written by Parliament and in some cases creates a framework that is used by secondary legislation which contains the actual details. A lot of this secondary legislation is written by the Executive branch of government (by civil servants in the appropriate branch of government) and may not involve any parliamentary oversight. Comparing the relative volume of primary/secondary legislation over time would show if the Executive branch was gaining more powers to write laws, at the expense of Parliament.

With all the interesting discussions going on, setting ourselves up and copying the data (from memory sticks, not the internet), coding did not really start until 11, and we had to have our projects ‘handed-in’ by 16:00, not enough time to be sure of getting even an approximate answer to the primary/secondary legislation question. So I plumped for solving a simpler problem that I was confident of completing.

Certain phrases are known to be frequently used in legislation, e.g., “for the purposes of”. What phrases are actually very common in practice? The domain experts were interested in phrases by branch of government and other subsets; I decided to keep it simple by processing every file and giving them the data.

Counting sequences of n words is a very well studied problem and it was straightforward to locate a program to do it for me. I used the Lynx web browser to strip out the html (the importance of making raw text available for this kind of analysis work was recognized and this will be available at some future date). I decided that counting all four word sequences ought to be doable on my laptop and did manage to get it all to work in the available time. Code and list of 4-grams over the whole corpus available on Github.

As always, as soon as they saw the results, the domain experts immediately starting asking new questions.

Regular readers of this blog will know of my long standing involvement in the structure and interpretation of programming language standards. It was interesting to hear those involved in the writing/interpretation of legislation having exactly the same issues, and coming up with very similar solutions, as those of us in the language standards world. I was surprised to hear that UK legislation has switched from using “shall” to using “must” to express requirements (one of the hacks plotted the use of shall/must over time and there has been an abrupt change of usage). One of the reasons given was that “must” is more modern; no idea how word modernness was measured. In the ISO standards’ world “shall” is mandated over “must”. Everybody was very busy in the short amount of time available, so I had to leave an insiders chat about shall/must to another time.

The availability of such a large amount of structured English documents having great import should result in some interesting findings and tools being produced.

Cobol 2014, perhaps the definitive final version of the language…

November 6th, 2014 No comments

Look what arrived in the post this morning, a complementary copy of the new Cobol Standard (the CD on top of a paper copy of the 1985 standard).

Photo of Cobol 2014 and 1985 Standards

In the good old days, before the Internet, members of IST/5 received a complementary copy of every new language standard in comforting dead tree form (a standard does not feel like a standard until it is weighed in the hand; pdfs are so lightweight); these days we get complementary access to pdfs. I suspect that this is not a change of policy at British Standards, but more likely an excessive print run that they need to dispose of to free up some shelf space. But it was nice of them to think of us workers rather than binning the CDs (my only contribution to Cobol 2014 was to agree with whatever the convener of the committee proposed with regard to Cobol).

So what does the new 955 page standard have to say for itself?

“COBOL began as a business programming language, but its present use has spread well beyond that to a general purpose programming language. Significant enhancements in this International Standard include:

— Dynamic-capacity tables

— Dynamic-length elementary items

— Enhanced locale support in functions

— Function pointers

— Increased size limit on alphanumeric, boolean, and national literals

— Parametric polymorphism (also known as method overloading)

— Structured constants

— Support for industry-standard arithmetic rules

— Support for industry-standard date and time formats

— Support for industry-standard floating-point formats

— Support for multiple rounding options”

I guess those working with Cobol will find these useful, but I don’t see them being enough to attract new users from other languages.

I have heard tentative suggestions of the next revision appearing in the 2020’s, but with membership of the Cobol committee dying out (literally in some cases and through retirement in others) perhaps this 2014 publication is the definitive final version of Cobol.

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The POPL 2015 papers involving C

November 4th, 2014 No comments

SIGPLAN (the ACM Special Interest Group on Programming LANguages) has just made available many of the papers that have been accepted for their 2015 POPL conference (Principles of Programming Languages). Good for them. I wish more conferences would do this.

There are three papers involving C, so obviously I have read those first. Two papers are heavy on the mathematics and one not quiet so heavy:

  • Sound Modular Verification of C Code Executing in an Unverified Context: Describes a tool that takes C source annotated with separation logic and translates it to C source containing runtime checks; it is intended that these runtime checks verify the conditions expressed in the separation logic. Why does the developer add the interface checks in separation logic and then translate, rather than adding them in C in the first place? This was question was not addressed
  • Common compiler optimisations are invalid in the C11 memory model and what we can do about it: This sounds like bad news, but the introduction mentions specialist optimizations that are common in that specialist area. There follows 11 pages of mathematics + another five pages in an appendix. Page 12 tells us what it is all about. Some requirements in C11 would be muck up the nice mathematics should CompCert, which currently supports C90, be upgraded to C11. In other words, a compiler implementor is complaining that wording in the standard is making their life difficult (hey, join the queue) and has published a paper about it.
  • Formal verification of a C static analyzer: An interesting piece of work spoiled by claims that a soap powder manufacturer would not be able to get away with. Verasco, the static analysis tool described, does its checking on an intermediate language that is two-steps removed from the original C source. Using the authors’ logic I could bolt on one of the existing Fortran-to-C translators and claim to have a formally-verified Fortran static analyzer, with C being just an intermediate language in the chain. The problem with analyzing an intermediate language is that the transformations that have occurred along the way have changed the semantics of the original code, so the results of any analysis could be different than if applied to the original source. An example from the paper, the code:
    z = f(x) + 2 * g(y)

    is transformed to:

    t1 = f(x); t2 = g(y); z = t1 + 2 * t2;

    The implementation thus selects one of the two possible evaluation orders for the functions f and g. It is possible that calling f before g will result in behavior that is different from calling g before f (no undefined behavior occurs because there is a sequence point before a function returns, using pre-C11 terminology).

    So Verasco is only checking one of the two possible execution paths in this code. Not a particularly sound proof.

    C-semantics is the C formal methods tool that stands head and shoulders above anything else that currently exists (a fun Fibonacci example). It is actually based on the C source and does significantly more checking than verasco, but is not mentioned in the “Related work” section of the paper.

Some of the other POPL papers look a lot more interesting and potentially useful.