Wickett, Karen M. “Discourse situations and markup interoperability: An application of situation semantics
to descriptive metadata.” Presented at Balisage: The Markup Conference 2010, Montréal, Canada, August 3 - 6, 2010. In Proceedings of Balisage: The Markup Conference 2010. Balisage Series on Markup Technologies, vol. 5 (2010). https://doi.org/10.4242/BalisageVol5.Wickett01.
Balisage: The Markup Conference 2010 August 3 - 6, 2010
Balisage Paper: Discourse situations and markup interoperability
An application of situation semantics to descriptive metadata
Karen Wickett
Doctoral Student
Graduate School of Library and Information Science at the University of Illinois
Urbana-Champaign
Interoperability is often considered a key issue for information systems, but there
are
many different kinds of interoperability and only a few have been give precise definitions.
Situation semantics and the notions of discourse situations and resource
situations are promising tools for the conceptualization of markup within a
general theory of communication. This paper uses these concepts to explore the role
of
context in determining the meaning of markup and to define a particular kind of
interoperability for markup structures. A Dublin Core OAI-PMH record and associated
schema
are used to show how the use of contextual information supports (or fails to support)
the
interoperability of the record.
Although context clearly influences how markup structures are deployed and how they
are
retrieved and processed, the ways that context determines the interpretation of markup
are not
well-understood or consistently conceptualized. The role of context has been acknowledged
in a
few narrow areas -- for example, in how it determines the grammatical mood of the
assertions
signaled by tags and the ontological status of XML documents (Renear 2003).
Context is an obvious part of markup systems, since processing any XML document requires
the
interplay of the document with structures and systems that are not part of the document.
A developed understanding of the role of context in markup can illuminate well-known
problems for information systems, particularly those associated with interoperability.
While
there is a general sense that interoperability is a sort of freedom from local context,
interoperability itself is not well-theorized in terms of markup structures and
interpretation. Preservation and portability of markup structures may be aided by
approaches
that operate in reference to the logical meaning of those structures (Dubin et al. 2003), but the reliance on the semantic meaning of structures presents a sort of boot-strapping
challenge since these interpretations must be determined at some point. Context (both
internal
and external to a document) will play an essential role in mapping from syntax into
semantics,
so we need a clear understanding of how context shapes the assignment of meaning to
markup
structures.
Wrightson has demonstrated how situation semantics (Barwise and Perry 1983) can provide
insights into the communication of information through markup structures (Wrightson 2001) and has presented a corresponding toolkit for the analysis of XML
documents as utterances (Wrightson 2005). Applying situation semantics to
markup is attractive since it is intended as a general account of communication and
so holds
the promise of integraing our understanding of markup meaning into a general theory
of
communication.
That much markup seems to function at least in some respects like a natural language,
rather than a formal language, makes the connection with theories of natural lanaguage
particularly promsing. Situation semantics is used here to support an account of the
assignment of meaning to markup structures; first through the definition of a particular
kind
of interoperability for markup structures and then in an examination of the role of
schema in
interoperability and interpretation.
Situation semantics supports a view of communication of information through markup
structures that gives explicit accounting for the context in which the record was
created and
in which it is interpreted. In what follows situation semantics is used to define
interoperability and to demonstrate how specific parts of Dublin Core OAI-PMH records
convey
contextual information that supports the interpretation of those records.
Situation Semantics and XML Metadata
This section briefly introduces concepts from situation semantics and shows how they
may
be applied to XML metadata.
Barwise and Perry apply situation semantics to the interpretation of natural language
utterances (Barwise and Perry 1983) by modeling the meaning of an indicative sentence as a
relation between a situation in which the sentence is uttered and a situation which
is
described by the utterance of the sentence. The position here is that since metadata
records
are sequences of indicative sentences, situation semantics can usefully explain the
ways in
which they carry meaning. An utterance situation is made up of a discourse situation and the speaker's connections (discussed in the following section). Any situation which uniquely
anchors the roles of a speaker, an addressee, a discourse location, and an expression
is
considered a discourse situation.
The technical notion of a situation here is very close to our intuitive one: a situation
occurs at a space-time location and involves individuals participating in certain
roles and
standing in relations. It also closely corresponds to the notion of a state of affairs, especially since situations are abstract objects that may or
may not obtain.
In the case of descriptive metadata the role of the speaker can be anchored to the
metadata creator at the time when the record is created. [1]In contrast, the role of the addressee is left open until the record is retrieved
and viewed by some consumer, and it is only at this point that all of the roles are
anchored
to form a complete discourse situation. The entire discourse situation will be extended
in
time and typically mediated through several computational environments. This extension
in time
is a primary motivator for interoperability efforts that are concerned with supporting
the
preservation (especially in the long term) of metadata records.
Since descriptive metadata records are created without specification of the addressee,
the
speaker and the addressee may be operating in very distinct environments. This kind
of
disparity is common in written communication, where an author and a reader may be
separated by
centuries or differences of language. Regardless, the differences between the environment
of a
speaker and an addressee of XML documents requires our attention in order to understand
the
contribution that elements of those environments make to the interpretation of documents.
The described situation for a metadata record is one in which a resource with each
of the
properties given in the record exists. The space-time location for this described
situation
will temporally precede and overlap the space-time location of the situation in which
the
record was created, since presumably a resource exists before it is described.[2] Hopefully the discourse situation that captures the communication of metadata will
fall entirely within the described situation that arises from that metadata, and consumers
are
able to access the described resource. But one can easily imagine cases where the
resource
indicated by the metadata record no longer exists at the time of the retrieval of
the record,
or it no longer has the properties indicated in the record (e.g. it is no longer accessible
through a given URL). It is also possible to imagine cases where the described situation
does
not obtain at all, since the record is simply erroneous. In any case, a record won't
facilitate communication and access to resources unless an addressee is able to interpret
it.
To ensure the operation of records and to support access, we need to understand what
goes into
the interpretation of descriptive metadata records.
Connections and Resource Situations
Situation semantics explicitly models of the compositionality of meaning by accounting for how the meaning of structures
that are part of an utterance make systematic contributions to the meaning of the
utterance
as a whole. Expressions that occur at one point in a discourse situation can supply
a
setting that influences how expressions that occur later
in the discourse situation are understood.
The speaker's connections in this model are an
assignment of referents to the expressions within an utterance. Since the speaker
and the
addressee in a discourse situation corresponding to a metadata record are far away
from each
other (in terms of space, time, and computational environments) the connections on
both
sides of the utterance require direct attention. In general, the goal of interoperability
is
for the speaker's connections to match the connections of the addressee for each expression
that makes up a record.
In XML records, it is relatively clear how the connections established by certain
parts
of a record determine how other parts of the record are to be processed or understood.
For
example, the connections given in the XML declaration provide a setting that constrains
how
the record is to processed. We can further divide this expression and focus on the
part that
leads (the "?" that immediately follows the opening bracket), which gives a setting
in which
the rest of the tag can be recognized as containing processing information.
The hierarchical nature of XML documents gives rise to a hierarchy of settings. The
primary setting is established by the XML declaration, which establishes that what
follows
is an XML document. Any further declaration of an associated schema or namespace will
also
establish a setting that influences how the expressions that occur within it are
interpreted. These schematic settings are secondary to the setting provided by the
XML
declaration since the context in which it is possible to process and use them is given
by
the fact that they occur within an XML document.
The settings are internal to an utterance, but context is external. The settings of
an
utterance indicate the resource situations necessary for
interpretation of a record. Resource situations are the situations that the actors
participating in a discourse situation have access to and use to identify and assign
connections for expressions. In this model, resource situations are naturally seen
as
supplying context for the creation or interpretation of markup. A resource situation
functions in this model to account for the specific elements of the environment that
a
metadata creator uses to assign meaning to markup and a consumer uses to intepret
that
markup.
Defining Descriptive Interoperability
While interoperability is frequently called upon as a motivating factor for improvement
in
information systems, it is not often given a systematic characterization within a
general
framework for description and communication. A working notion of interoperability
for
descriptive metadata in XML (inspired by (Sperberg-McQueen, et al. 2000), (Renear, et al. 2002) and in line with the OAIS Reference Model (Lavoie 2004)) is that an interoperable description is one that supports licensing
the same set of assertions in any environment.
In terms of situation semantics then, an interoperable description is one for which,
given
any addressee, the the set of connections that link expressions to their referents
remains
fixed. Interoperability then can be viewed as a kind of independence from particular
features
of the discourse situation. The time or location associated with the utterance of
an
interoperable description can vary without a change in the meaning of the utterance.
In order
to achieve this kind of interoperability, metadata creators must either convey these
connections explicitly, or supply enough information to allow a user to discover the
intended
connections. Unless connections are given in (or pointed to by) a record, someone
trying infer
information from the document is left to determine connections on her own.
Of course, such a reader will not be entirely on her own. She can still use her background
knowledge, and given a record that is human-readable, she might have a fair degree
of success.
But she would have to rely on a larger set of resource situations to establish connections
for
the expressions in the record than in a case where connections are explicitly given.
In fact, resource situations that supply the information necessary to process or interpret
XML metadata will always be a requirement for determining the assertions licensed
by a
document. Grasping the intended connections for records requires a certain set of
knowledge
about the conventions in play, so it is unrealistic to expect a descriptive record
to be fully
interoperable as given above. This suggests an adjustment to the definition of
interoperability, and characterizing it as an effort to reduce the burden of gaining
access to
the resource situations required to fully interpret a record.
Example: Analyzing a Dublin Core OAI-PMH Record
Figure 1 shows part of an XML record retrieved from an OAI server.
As discussed above, since this is an XML document, the primary setting for the record
is given
by the XML processing instruction. This expression indicates connections that establish
how
the document is to be processed or interpreted. A secondary setting can be identified
by
examining the attributes within the root "OAI-PMH" element for the record.
The schema location attribute within the "OAI-PMH" tag acts as a pointer to documentation
that specifies a certain kind of connections for child elements that follow this element.
These connections provide the vocabulary and structural constraints for tags and attributes,
and they may be overridden by further schema declarations within a child element.
In this
case, while the OAI-PMH.xsd document does give instructions for the construction of
valid
OAI-PMH documents by giving structural and datatype restrictions, it does not give
the full
intended semantics for tags that conform to it.
A third setting is given in this example by the namespace and schema attributes in
the
"oai_dc" element. As above, the schema location attribute points to documentation
that
specifies syntactic connections for the child elements. The connections given here
override
the those given in the OAI-PMH element. This means that the connections for "identifier"
within the "oai_dc" element correspond to the Dublin Core Element Set, whereas the
occurrences
of "identifier" elements higher up in the record have the connections established
by
OAI-PMH.
The oai_dc.xsd documentation imports simpledc20021212.xsd, and therefore does provide
access to the resource situation necessary to make the correct connections for element
names
in the core element set for Dublin Core. Each of the element names that appear within
the
third setting are defined in this documentation through marked-up annotations. In
contrast,
OAI-PMH.xsd only gives syntactic information and processing instructions. The intended
semantics for OAI element names such as "identifier", "record", or "metadata" are
not provided
in the documentation itself, nor is there any reference (network locatable or otherwise)
to a
source for definitions of these terms. These terms are defined in the protocol documentation,
but it is not clear how an addressee (reader/consumer) of the record could reach that
documentation without additional information or direction.
The OAI Identifier
An "identifier" element within a OAI-PMH record is specified by the documentation
given
in OAI-PMH.xsd as occurring within a "header" element and as containing a URI. However,
there is no direct indication of what the given identifier serves to identify. A user
of
this record can rely on the nesting of the element within the "header" of the "record"
element to infer that the identifier serves to identify the record. Or they could
use their
knowledge that the record contains metadata about a resource to infer that the identifier
picks out a resource that has all of properties indicated within the "metadata"
element.
In fact, some services that convert OAI-PMH records in RDF take the second approach
and
use the OAI identifier as a subject URI for statements about a resource that are derived
from the record. However, the OAI Protocol for Metadata Harvesting states that "the
identifier described here is not that of a resource. The nature of a resource identifier is outside the scope
of the OAI-PMH" (Lagoze, et al. 2002 emphasis original). Rather, this identifier
picks out the OAI Item, which is a conceptual container for metadata.
This is a failure of interoperability. The RDF that result from this kind of
transformation are intended to make statements about a resource, but they will actually
be
making erroneous statements about a metadata container. Thus the assertions licensed
by
markup in the environment of the addressee who has transformed the description will
differ
significantly from the assertions licensed in the environment of the speaker who issued
the
original record. The resource situation in use by the transformation was incomplete
with
respect to the connections for the OAI identifier, and an error resulted. The connections
used in the generation of the OAI record did not match the connection used to transform
the
record into RDF. This kind of a failure of interoperability is common and well-known,
and
situation semantics provides a systematic framework in which to understand it.
Discussion
The meaning of markup structures can be modeled by representing the set of inferences
that
are licensed from a document (Marcoux et al. 2009), and the OAI markup vocabulary
specifically has been given such an interpretation (Sperberg-McQueen 2005). However,
such an approach assumes an unambiguous mapping from tags to the logical predicates
associated
with those tags. The formal tag set description approach does not directly address
how meaning
is constructed by a reader who encounters an XML document "in the wild", especially
when that
reader was not privy to the development of the vocabulary in use by the document.
An
overarching theory of communicative meaning like situation semantics can help us grasp
the
role that a formal tag set description plays when one is available, and see what is
missing
when that information is not available.
The use of natural-language identifiers for element names allows readers to interpret
markup by exploiting the everyday resource situations that constantly support language-based
communication (Wrightson 2005). But, as we demonstrated above with the case of
the OAI identifier, the name of a tag alone does not always convey everything necessary
to
properly interpret the logical meaning of corresponding markup. The problems that
arise for
this kind of mis-interpretation become obvious when the markup is used to derive RDF
that
makes incorrect logical statements.
The lack of access to documentation that explains the intended semantics for tags
is an
aspect of what has been called the documentation problem
(Sperberg-McQueen and Miller 2004). The issue could be addressed by sufficient access
to documentation (prose or computational) that describes the resource situation against
which
markup was created, to allow readers of the documents to establish connections to
interpret
the document correctly. Without such support, interoperability across time and systems
is an
unlikely prospect.
Acknowledgements: I would like to thank Allen Renear, Ingbert Floyd, and members of
the
Conceptual Foundation Group at GSLIS for comments and support in developing this paper,
and
Richard Urban for bringing the example of the OAI identifier to my attention.
References
[Barwise and Perry 1983] Barwise, J. and Perry,
J.Situations and Attitudes (1983). MIT Press, Cambridge,
MA.
[Dubin et al. 2003] Dubin, David, C. M.
Sperberg-McQueen, Allen Renear, and Claus Huitfeldt (2003). “A Logic Programming Environment
for Document Semantics and Inference,” Journal of Literary and
Linguistic Computing, 18:1, 39-47. doi:https://doi.org/10.1093/llc/18.1.39.
[Lagoze, et al. 2002] Lagoze, Carl, Herbert Van de
Sompel, Michael Nelson, and Simeon Warner, ed. 2002. The Open Archives Initiative
Protocol for
Metadata Harvesting. Protocol Version 2.0 of 2002-06-14. Document Version
2008-12-07T20:42:00Z. Open Archives Initiative, 2002.
http://www.openarchives.org/OAI/2.0/openarchivesprotocol.htm
[Renear, et al. 2002] “Towards a Semantics for XML
Markup.” Renear, Allen H., David Dubin, C. M. Sperberg-McQueen, and Claus Huitfeldt.
In R.
Furuta, J. I. Maletic, and E. Munson, (Eds.), Proceedings of the 2002
ACM Symposium on Document Engineering, (pp. 119-126), McLean, VA, November. New
York: Association for Computing Machinery (2002). doi:https://doi.org/10.1145/585058.585081.
[Renear 2003] Renear, Allen H. “Text from Several
Different Perspectives, the Role of Context in Markup Semantics.” Proceedings of the
2003
Conference on Computers, Literature, and Philology. Florence: University of
Florence.
Dubin, David, C. M.
Sperberg-McQueen, Allen Renear, and Claus Huitfeldt (2003). “A Logic Programming Environment
for Document Semantics and Inference,” Journal of Literary and
Linguistic Computing, 18:1, 39-47. doi:https://doi.org/10.1093/llc/18.1.39.
Lagoze, Carl, Herbert Van de
Sompel, Michael Nelson, and Simeon Warner, ed. 2002. The Open Archives Initiative
Protocol for
Metadata Harvesting. Protocol Version 2.0 of 2002-06-14. Document Version
2008-12-07T20:42:00Z. Open Archives Initiative, 2002.
http://www.openarchives.org/OAI/2.0/openarchivesprotocol.htm
Lavoie, B. (2004) "The Open Archival
Information System Reference Model: Introductory Guide" Microform and
Imaging Review, 33:2, 68-81. doi:https://doi.org/10.1515/MFIR.2004.68.
Marcoux, Yves, C.M.
Sperberg-McQueen, and Claus Huitfeldt “Formal and informal meaning from documents
through
skeleton sentences” in Balisage: The Markup Conference 2009 Proceedings, Montreal,
Canada.
2009. doi:https://doi.org/10.4242/BalisageVol3.Sperberg-McQueen01.
“Towards a Semantics for XML
Markup.” Renear, Allen H., David Dubin, C. M. Sperberg-McQueen, and Claus Huitfeldt.
In R.
Furuta, J. I. Maletic, and E. Munson, (Eds.), Proceedings of the 2002
ACM Symposium on Document Engineering, (pp. 119-126), McLean, VA, November. New
York: Association for Computing Machinery (2002). doi:https://doi.org/10.1145/585058.585081.
Renear, Allen H. “Text from Several
Different Perspectives, the Role of Context in Markup Semantics.” Proceedings of the
2003
Conference on Computers, Literature, and Philology. Florence: University of
Florence.
Sperberg-McQueen,
C.M., Claus Huitfeldt and Allen H. Renear (2000) "Meaning and interpretation of
markup."Markup Languages: Theory and Practice,
2:3. doi:https://doi.org/10.1162/109966200750363599.