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The Prisoner: Number 6[ Part 2 in a 3 part series. Last time we talked about some general characteristics of identifiers for legislation, and some sources of confusion in legacy systems. This time: some design problems having to do with granularity and use, and the fact that identifiers are situated in legal and bureaucratic process. ]

Identifier granularity

How small a thing should we try to identify? It’s difficult to make general prescriptions about that, for needs vary from corpus to corpus.  For the most part, we assume that identifier granularity should follow common citation or cross-referencing practice — that is, the smallest thing we identify or label should be the smallest thing that standard citation practice would allow a user to navigate to.  That will vary from collection to collection, and from context to context. For example, it’s quite common for citation to the US Code to refer to objects at the subsection level, sometimes right down to the paragraph level.  On the other hand, references to the Code in the Parallel Table of Authorities and Rules generally refer to a full section.  Similarly, although cross-references within the Code of Federal Regulations can be very granular, external references typically target the Part level. In any corpus, amendments can be expressed in ways that are very granular indeed.

Our citation and cross-referencing practices have evolved in the context of print, and we may be able to do things that better reflect the dynamic nature of legislative text.  The move from print to digital overturns background assumptions about practicality.  For example, print typically makes different assumptions about identifier stability than you would find, say, in an online legislative drafting system.  Good examples of this are found in citation practice for the Code of Federal Regulations, which typically cites material at the Part level because (one imagines) changes in numbering and naming of sections are so frequent as to render identifiers tied to such fine divisions unstable — at least in print, where the shelf life of such fine-grained identifiers is shorter than the shelf life of the edition by an order of magnitude. In a digital environment, it is possible to manage identifiers more closely, permitting graceful failure of those that are no longer valid, and providing automated navigation to things that have moved. We look at some of the possibilities and implications in sections on granularity, fragmentation, and recombination below.  All of those capabilities carry costs, and over-design is a real possibility.

Metadata, markup, and embedding

Thinking about granularity leads to ideas about the linkages between metadata and the target object itself.  Often metadata applies to chunks of documents rather than whole documents.  Cross-referencing in statutes and legislation is usually done at the subdocument level, for instance, and subject-matter classification of a bill containing multiple unrelated provisions would be better if the subject classifications could be separately tied to specific provisions within the bill. That need becomes particularly acute when something important, but unrelated to the main purpose of the bill, has been “snuck in” to a much larger piece of legislation.  A stunning example of such a Frankenstein’s monster appears at  111 Pub. L. 226 . It is described in its preamble as modernizing the air-traffic control system, but its first major Title heading describes it as an “Education Jobs Fund”,  and its second major Title contemplates highly technical apparatus for providing fiscal relief to state governments.

We are aware that sometimes we are thinking in terms that are not currently supported by the markup of documents in existing XML-creating systems.  However, we think it makes sense to design identifier systems that are more capable than some document collections will currently support via markup, in the expectation that  markup in those collections will evolve to the same granularity as current cross-referencing and citation practice, and that point-in-time systems supporting the full lifecycle of legislative drafting, passage, and codification will become the norm.  Right now,  divisions of statutory and regulatory text below the section level (“subsection containers”) are among the most prominent examples of “missing markup”; they are provided for in the legislative XML DTDs at (eg.), but do not survive into the FD/SYS versions from GPO.

Most often, we imagine that the flow of document processing leads from markup to metadata, since as a practical matter a lot of metadata is generated simply by extracting text features that have been tagged with some XML or HTML element.  Sometimes the flow is in the other direction; we may want to embed metadata in the documents for various purposes.  Use of microformats, microdata, and other such schemes can be handy for various applications; the use of research-management software like Zotero, or the embedding of information about document authenticity comes to mind.  These are not part of a legislative data model per se, but represent use cases worth thinking about.

Stresses and strains

Next, we turn to things that affect the design of real-world identifier systems, perhaps rendering them less “pure” in information-design terms than we might like.

Semantics versus purity

Some systems enforce notions of identifier purity — often defined as some combination of uniqueness, orderliness, and ease of collation and sorting — by rigorously stripping all semantics from identifiers.  That is an approach that can function reasonably well in back-end systems, but greatly reduces the usefulness of the identifiers to humans (because understanding what the identifier identifies requires database reflection), and introduces extra possibilities for error in application because (among other reasons) errors caused by human transcription are hard to catch when the identifiers are meaningless strings of letters and numbers.  On the other hand, “pure” opaque identifiers counter a tendency to assume that one knows what a semantically laden identifier means, when in fact one might not.  And sometimes opaque identifiers can be used to provide stability in situations where labels change frequently but the labelled objects do not.  

At the other end of the spectrum, identifier systems that are heavily burdened with semantics have problems with uniqueness, length, persistence, language, and other issues arising from inherent ambiguity of labels and other home-brewed identifier components.  It is worth remembering, too, that one person’s helpful semantics are another’s mumbo-jumbo; just walk up to someone at random and ask them the dates of the 75th Congress if you need proof of that. Useful systems find a middle ground between extremes of incomprehensible rigor and mindlessly verbose recitation of loosely-constructed labels.

It’s worth noting in passing that it can be very difficult to prevent the unwanted exposure of “back-end” identifier to end users.  For example, URIs constructed from back-end components often find their way into the browser bars of authors researching online, who then paste them into documents that would be better served by more brain-compatible, human-digestible versions.

Moniker type Identifier Notes
Citation 18 USC 47 Standard citation ignores all but Title and section number; intermediate aggregations not needed, and confusing.
Popular name Wild Horse Annie Act Descriptive and often used in popular accounts, the press, agency guidance on related rules, etc., but hard to find in the codified version.
LII URI, (“presentable” version) Based on title and section number
LII URI, “formal” version—-000-.html Also title and section based, but padded and normalized to allow proper collation; “supersection” aggregations above the section level are similarly disambiguated.
USGPO URI, GPOAccess Parameterized search returning 1 result.
FindLaw URI Seemingly mysterious, because it interjects subtitle and part numbering, which is not used in citation.  Note that this hierarchy would also vary from Title to Title of the Code — not all have Subtitles, eg.

The table above shows some “monikers in the wild” — various real-world approaches to the problem of identifying a particular section of the US Code.  The “formal” LII identifier, highlighted in yellow, shows just how elaborate an identifier needs to be if it is to accommodate all the variation that is present in US Code section numbering (there is, for example, a 12 USC 1749bbb-10c), while still supporting collation.  The FindLaw URI demonstrates the fragility of hierarchical schemes; the intermediate path components would vary enormously from Title to Title, and occasionally lead to some confusion about structure, as intermediate levels of aggregation are called different things in different Titles. It is hard to tell, for example, if Findlaw interpolates “missing” levels into the URIs in order to maintain an identical scheme across Titles with dissimilar “supersection” structure.

Administrative zones of control and procedural rules

Every identifier implies a zone of administrative control:  somebody has to assign it, somebody has to ensure its uniqueness, and somebody or something has to resolve it to an actual document location, physical or electronic.  Though it has taken years, the community has recognized that qualities of persistence and uniqueness are primarily created by administrative rather than technical apparatus.  That becomes a much more critical factor when dealing with government documents, which may be surrounded by legal restrictions on who may assign identifiers and when, and in some cases what the actual formats must be.  A legislative document may have its roots in ideas and policies formed well outside government, and pass through numerous internal zones of control as it makes its way through the legislature. It may emerge at the other end via a somewhat mysterious intellectual process in which it is blown to bits and the fragments reassigned to a coherent, but altogether different, intellectual structure with its own system of identifiers (we call this ‘codification’).  There may be internal or external requirements that, at various points in the process,  cause the document to be expressed in a variety of publications and formats each carrying its own system of citations and identifiers.

The legacy process, then, is an accretive one in which an object acquires multiple monikers from multiple sources, each with its own requirements and rules.  Sometimes those requirements and rules are shaped by concerns that are outside, and perhaps at odds with, sound information-organization practice.  

For example, the House and Senate each have their own rules of procedure, in which bill numbering is specified.  Bill numbers are usually accession numbers that reset with each new Congress, but the rules of procedure create exceptions.  Under the rules of the House for  the 106th Congress, the first ten bill numbers were reserved for use by the Speaker of the House for a specified time period. During the 107th and 108th Congresses (at least), the time period was extended to the full first session.  We surmise that this may have represented an attempt to reserve “important” bill numbers for things important to the majority party’s legislative agenda.  Needless to say, this rendered any relationship between bill numbers and chronology or order of introduction questionable, at least in a limited number of cases. The important point is that identifier usage will be hostage to political considerations for as long as it is controlled by rules of procedure; that situation is not likely to change.  

But there are also virtues to the legacy process, primarily because close association with long-standing institutional practices lends long-term stability to identifier schemes.  Bill numbers have institutional advocates, are well-understood, and unlikely to change very much in deployment or format. They provide good service within their intended scope, however much they may lose when taken outside it.

That being said, a “gold standard” system of identifiers, specified and assigned by a relatively independent body, is needed at the core.  That gold standard can then be extended via known, stable relationships with existing identifier systems, and designed for extensible use by others outside the immediate legislative community.

Status, tracing, versioning and parallel activity

It is useful to distinguish between tracing the evolution of a bill or other legislative document and recording the status of that document.  Status usually records a strong association between some version of the document and a particular, well-known stage or event in the process by which it is created, revised, or made binding.  That presents two problems.  There is a granularity problem, in that some legislative events that cause alteration of the document are so trivial that to distinguish all of them would be to create an unnecessarily fine-grained, burdensome, and unworkable system. There is a stability problem in that legislative processes change over time, sometimes in ways that are very significant, as when (in 1975) the House rules changed to allow bills to be considered by multiple committees, and sometimes in ways that are not, as when House procedural rules are revised in trivial, short-lived ways at the beginning of each new Congress.  Optimally, bill status would be a property related to a small vocabulary of documented legislative milestones or events that remains very stable over time.  Detailed tracing of the evolution of a bill would be enabled through a series of relationships among documents that would (for instance) identify predecessor and successor drafts as well as other inter-document relationships.  These properties would exist as part of the data model without need for additional semantics in the identifiers. Such a scheme might readily be extended to accommodate the existence of multiple, parallel drafts, as sometimes happens during committee process.

In this way, the model would answer questions about the “version” of a given document by making assertions either about its “status” — that is, whether it is tied to some well-known milestone in legislative process — or by some combination of properties that are chained back to such a milestone.  For example, a document might be described as a “committee draft from Committee X that is a direct revision of the document submitted to the committee, dated on such-and-such a date”.  The exact “version” of the document is given by a chain of relationships tied back to a draft that can be definitively associated with a stable milestone in the legislative process.

It’s worth noting that while it would certainly be possible to identify versions using “version numbers” built out by extending the accession number of the root document with various semantically-derived text strings, it’s not necessary to do so.  The identifiers could, in fact, be anything at all.  All that is needed is for them to be linked to well-known “milestone” documents (e.g., the version reported out of committee) by a chain of relationships ( for example,  “isSuccessorVersionOf”) that chain back to the milestone.  This may be particularly important when the document-to-document relationship extends across boundaries between zones of administrative control, or outside government altogether.


To a great extent, the things that are being ‘identified’ by identifiers are discrete documents, traditionally rendered as discrete print works. There are, however, significant exceptions that should be accommodated. In addition, changes in the nature and structure of documents that may be issued in the future should be anticipated as well.

The issue of “granularity” arises from the need to identify parts of a discrete document. For example, although a congressional hearing is published as a single document (sometimes in multi-volume form), it may be useful to make specific references to the testimony of individual witnesses. Even more significant would be mapping the relationships between the U.S. Code and the public laws from which it is derived. In these cases, the granularity of the identifiers available should be more fine-grained than the documents being identified. So, although a Public Law or slip law can be completely identified and described by a given set of identifiers, it is valuable to have additional identifiers available for sub-parts of these documents, so that mapping adequate relationships to sections of the U.S. Code can be described.

Of course, admitting such identifiers can be a slippery slope. The set of things that could be identified in legislative documents is fairly unbounded, and any identifiers will arguably be useful to someone. An attempt to label all possible things, however, is madness, and should be avoided. The result would be numbers of unused, or seldom used identifiers which would over-complicate entities and the overall structure of the identifier system.

Fragmentation and recombination

Identifiers are used in ways that go well beyond slapping a unique label on a relatively static document.  They help us keep track of resources that can, in the electronic environment, be highly mobile.  Legislation is often fragmented and re-combined into new expressions, some official and some not.  For many legal purposes, it is important for the fragments to be recognized as authentic, that is, carrying the same weight of authority as the work from which they were originally taken.  Current practice accommodates this through the use of a variety of officially-published finding aids, including significant ones associated with the US Code:  the Table of Popular Names, the “Short Title” notes, and Table III of the printed edition of the US Code, which is essentially a codification map. Elsewhere, we’ve referred to such a work as a “pont”, that is, something that bridges two isolated legal information resources.  Encoding  of ponts in engineered ways that facilitate use in retrieval systems is a particularly crucial function that should be supported by the identifier model. 


Codification presents challenges, the more so because it can erect substantial barriers for inexperienced researchers.  Citizens often seek legislation by popular name (“Wild Horse Annie Act”). They don’t get far.  The problem is usually (though not always) more difficult than simply uncovering an association between the popular name of the act they’re seeking and some coherent chunk of the United States Code, or a fragment within a document that carries a Public Law number.  Often, the original legislation has been codified in ways that scatter fragments over multiple Titles of the US Code.

That is so because even a coherent piece of legislation — and many are not —  typically addresses a bundle of issue-related concerns, or the needs of a particular constituency.  A “farm bill” might contain provisions related to tax, land use, regulation of commodities, water rights, and so on.  All of those belong in very different places under the system of topics used by the US Code.  Thus, legislation is fragmented and recombined during the process of codification.  While this results in much more coherent intellectual organization of statutes over the long term, it makes it difficult for users to exchange the tokens they have — usually the popular name of an Act, or some other moniker assigned by the press (“Obamacare”) — for access to what they are seeking.

Table III of the United States Code provides a map from provisions of Public Laws to their eventual destination within the US Code, as the Code existed at the time of classification.  That is potentially very useful to a present-day audience, provided that the relationships expressed in it can be traced forward through time; changes to the Code from the time of classification forward  would need to be accounted for.  That would rest on two things:  an identifier system capable of tracking the fragments of the original Act as they are codified, and a series of relationships that account for both the process of codification and the processes by which the Code itself subsequently evolves.

Fragmentary re-use

Codification is really a special case of something we might call “fragmentary re-use” — an application in which a document snippet, or other excerpt from an object, is reused outside its parent.  Next time, we’ll discuss the problems of identifier exposure in a Linked Data context, noting that identifiers must carry their own context.  A noteworthy example of this is the legislative fragment that needs to carry some link back to its provenance, and specifically its legal status or authority.  Minimally, this would be an identifier resolvable to a data resource describing the provenance of the fragment.  Such an approach might fit well into a “layered” URI scheme such as that used by

[ Fragmented and recombined as we are, we’ll stop here with a song about codification, a granular, highly-recombinant and NSFW musical selection, and a third that queries the object itself (at 2:45) and makes heavy use of visual and audio recombination . Next time: some problems with current practice, identifier manufacturing, and what happens when we think about Linked Data, as we surely should ]

[NB: Making MetaSausage is a new blog on legislative metadata and legislative systems.  It’s a place to talk geek about legislation.  We make no promises, but we think posts will appear every couple of weeks.  Comments encouraged. ]

The Prisoner: Number 6The law-creating process described in How Our Laws Are Made (HOLAM), and other civics texts like it, is a lot like the Mississippi River:  formed out of a zillion small tributaries, many of them nameless, joined into a stream that passes through a number of jurisdictions and has lots of side passages, loops and eddies, eventually breaking up again into a series of tiny streams passing through a delta.   There is a central part of the process  — the mainstream — that is fairly well mapped, with placenames and milestones that are pretty well understood.  There are hundreds of smaller streams and brooks at either end of the process that are not well understood or named at all, and a few places in the middle where the main stream branches unpredictably.  It is a complicated map, and it describes a territory where many people, places and things are named  — but  many are not, and some are named in ways that are ambiguous, confusing, or conflicting.

This post is about identifiers, and particularly document identifiers : snippets of text that uniquely identify  documents that are either generated by the legislative process or are found in its vicinity.  That idea is simple enough. But well-thought-out, carefully constructed identifiers are an important foundation of any data model — and are surprisingly difficult to design.  Legislative data models have (at least) two purposes:  first, they are a kind of specification that precisely describes data encountered in and around the legislative process, the precise relationships among the data items and elements, and (significantly) relationships between the data and the real-world people, groups, and processes that create and manipulate the data.  Second, they are a device to enable communication among system-builders, stakeholders, and users about what is to be collected, what is to be expressed or retrieved, and so on.   Before any of that can be built in a way that is both precise and communicative, we must be sure of what exactly we are talking about.  Identifiers should answer that question — what the hell are we talking about? — unambiguously.   Or at least we would like them to.  Often, our legacy identifier systems don’t do that very well.  As we shall see,  many existing identifier schemes are burdened with competing constraints and conflicting expectations, with less-than-ideal results.

What do identifiers do?

In print, identifiers have worked differently than we really want them to in an electronic environment.  The conventions of printed books — use of pagination, difficulty of recall once issued, relative stability of editions, and most of all the assumption that identifiers will be interpreted by human readers with some knowledge of their context and purpose — result in identifiers that are less rigorous than what we need in a world of granular data consumed and processed by machines.  Some illustrations are found below. In reality our legacy “identifiers” are often less-rigorous monikers serving multiple functions, and in a digital environment we must unpack them into separate items with separate functions.  Here are some of the functions:

a) Unique naming.  The diverse monikers that document creators and administrators use in current practice are supposed to provide unique names for documents.  Sometimes they do; often they don’t.  Usually that is because a moniker that is unique within a particular scope loses uniqueness in some wider, unanticipated arena. That is especially likely to happen when a collection of objects is moved from its original, intended scope on to the open Web, but you can find examples closer to home.  A Congressional bill number is a good example: it is unique only within the Congress during which it was assigned.  There might be an “H.R. 1234” for several Congresses; “108 H.R. 1234” is made unique by the addition of the number of the Congress during which it was introduced.  Of course, human error is often at fault, as when (for one year in the mid-1990s), there were two very different section 512s in Title 17 of the US Code.   

b) Navigational reference.  Identifiers often serve as search terms or convenient handles for taking the reader to another document, or for retrieving it (we discuss retrieval in the next section).  Standard caselaw citation practice is a special case of this, created specifically for printed books.  In that legacy context, unique identification and citation functions are often run together badly, usually because numbered pages are not sufficiently granular to uniquely identify individual items.   For example, two briefly-reported judicial opinions might well appear on the same page of a print reporter, and thus carry an identical citation.  The citation is then a perfectly good tool for navigating to each case within a series of printed volumes, but is not a unique name or identifier for either of them.   A look at will show that numerous cases, each quite short, originally appeared on page 421 of Volume 173 of West’s Federal Reporter, 3rd Series.   A sample is here: .  Any of the cases listed might be cited as 173 F.3d 421.

c) Retrieval hook/container label.   Here, we distinguish use of a citation as a retrieval hook from its use as a navigational device. As we make our way around the Web, that distinction is usually blurred. Following a link to its destination puts a chunk of text in front of our eyes, and so it’s hard to remember that the link might refer to the contents of a container for which it also provides a label, rather than to a simple destination milestone.  

To make the distinction clear, it’s useful to think about incorporation-by-reference or other forms of embedding.  Suppose that we wish to present the current text of a subsection of a statute inside some other online document — a citizen’s guide to Social Security benefits, for example.  We would likely do that via machine retrieval of the particular statutory subsection based on its identifier — but our goal would be to summon up a chunk of text, not navigate to a particular destination.  Put another way, our current practice conflates the use of citation as a means of identifying a point, milestone, or destination in a document (a retrieval hook) with a means of identifying a labelled subdocument that can be referenced or retrieved for other purposes ( a container label).

As an example, the THOMAS pages for individual bills and resolutions aggregate a great deal of information from the Congressional Record (CR), linking from the Bill Summary ‘Actions’ to both a textual representation of the CR page beginning with the desired text (but sometimes extending past the desired text into other information about unrelated issues) as well as a PDF representation of the page which shows the whole page (where the desired text may start towards the end, plus subsequent pages if the relevant section extends past the initial page).

For a specific example of this, the Lily Ledbetter Fair Pay Act of 2009 has a list of major actions on Thomas, one of which is a “motion to proceed to consideration of measure withdrawn in Senate” on Jan. 13, 2009.  The link for information on that motion is to CR S349: a specific page of the Congressional Record. Invoking that link leads to this display:

The Thomas page lists the four items on the particular Congressional Record page, the last of which is the item sought.  When that item is invoked a default page with the specific text of the motion is retrieved, but an additional link to the PDF version of that page can be viewed via a link at the head of the text, with the Lily Ledbetter motion at the bottom of the retrieved PDF.

d) Thread tag/associative marker.   Some monikers group related documents into threads — aggregations whose internal arrangement is implicitly chronological.  An insurance company claim number is, in exactly this way, a dual-purpose tool.  On the one hand, it refers uniquely to a document (a claim form) that you submit after your fender-bender.  On the other, the insurance company tells you that you must “use this claim number in all correspondence”  — that is,  use it to prospectively tag related documents.  That creates a labelled group of documents. If we then sort the group chronologically, it becomes a kind of narrative thread.  

In this way, the moniker implies a relationship between the documents without explicitly naming or describing it, as well as being pressed into service as the identifier for one or more documents in the cluster. Regulatory docket numbers function in this manner. That is intentional, because dockets are meant to be gathering places for documents. What is confusing  — and important to remember — is that a moniker that uniquely identifies a process — a regulatory rulemaking — has been bent to identify a collection of items associated with that process, and neither the association, the collection of items, nor any particular document have been uniquely identified.

Another conceptually-related but distinct example of this is the use of “captive search” URIs to meet a user’s need to dynamically assemble a set of related documents. For instance, one can retrieve all the environmental law decisions of the Supreme Court at this link:

Such URIs embed search terms (“environment”, “environmental”, “EPA”) and, when used in links, retrieve the set of documents found by searching on those terms.  Typically, they are used to deal with instability or growth in the underlying corpus of things being searched. They are “automatically” kept up to date as the collection changes, inasmuch as they just provoke a search of the changed collection that presents results based on the current collection contents.

In that way, they are a great help to site designers. Problems can arise, however, if the user imagines that the URI somehow identifies the exact set of items retrieved for any time period other than the moment of retrieval. Precisely because the method is dynamic, the user may or may not retrieve the same document set at a later invocation.   As a low-cost, low-effort alternative to semantic tagging, however, the approach is irresistible.  

Some newer systems,  such as VIAF, do allow the ad-hoc construction of URIs for dynamically assembled sets of objects that are then fixed as a permanent group identified by the newly-minted URI. Assuming that an appropriate search could be designed, one might thus construct URIs for any useful group of items found in an authority file, for example a list of all subcommittees of the House Armed Services Committee that have existed up to the present:

e) Process milestone.  The grant of a moniker by an official body can be an acknowledgement that official notice must now be taken, or that some process has begun, ended, or reached some other important stage.  That is obviously the case with bills, where a single piece of legislation may receive a number of identifiers as it makes its way through the process, culminating in a Public Law number at the time of signing. The existence of such a PL number can be taken as evidence that the bill has been passed into law.

f) Proxy for provenance.  Again because monikers are often assigned by officials or organizations with special standing, they become proxies for provenance.  The existence of a bill number is evidence that the Clerk of the House has seen something and acted in a particular way with respect to it; it is valuable evidence in any attempt to establish authority.

g) Popular names, professional terms of art, and other vernacular uses.  Monikers notably find their way into popular and professional use, some in ways that are quite persistent.  News media frequently refer to legislation by a popular name created by Congress based on the names of sponsors (the “Taft-Hartley Act”) or by the press itself (“Obamacare”).  They can be politicized (“death tax”), or serve as a kind of marketing tool (“USA-PATRIOT Act”). Some labels and identifiers become very closely associated with the things they label, becoming terms of art in their own right.  Thus, it is common to refer to a “501(c)(3) nonprofit” or a “Subchapter K”  partnership.  Vernacular labels have particular importance for citizens, who often use them as input to search systems.  At this writing, developers at the Sunlight Foundation have just started an initiative to collect such labels through crowdsourcing.

We’ll break off here with a musical selection or two.

[Next time: identifier granularity and some other characteristics; stresses and strains on identifier design.]

Some other reading you might find useful: