Reformatting, instead of being a last resort as material physically collapses, will be a common way of life in the digital age.

• disk to disk
• format to format

• define intellectual content concretely;
• specify how to check it operationally.

• digital information
• SGML or XML markup*

Two points deserve special attention: we expect programs to be capable of expressing a meaning and we want to be able to compare meanings. Unless we are very careful, we may very soon be forced to consider an endless chain of questions: what is the meaning of ...? what is the meaning of the meaning of ...? etc. Without going into a philosophical discussion of issues certainly transgressing any reasonable interpretation of the title of this book, we shall accept that the meaning of A is the set of sentences S true because of A. The set S may also be called the set of consequences of A. Calling sentences of S consequences of A underscores the fact that there is an underlying logic which allows one to deduce that a sentence is a consequence of A.

Usually the A itself is a set of sentences, thus we are saying in fact that the meaning of a set of sentences is the set of consequences that are deducible from it.

... we shall accept that the meaning of A is the set of sentences S true because of A. The set S may also be called the set of consequences of A. Calling sentences of S consequences of A underscores the fact that there is an underlying logic which allows one to deduce that a sentence is a consequence of A.

<OAI-PMH xmlns="http://www.openarchives.org/OAI/2.0/" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/
  http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd">
  <responseDate>2002-05-01T19:20:30Z</responseDate>
  <request verb="GetRecord" 
    identifier="oai:arXiv.org:hep-th/9901001"
    metadataPrefix="oai_dc"
    >http://an.oa.org/OAI-script</request> 
  <GetRecord>
    <record>
      ...
    </record>
  </GetRecord> 
</OAI-PMH>

This verb is used to retrieve an individual metadata record from a repository. Required arguments specify the identifier of the item from which the record is requested and the format of the metadata that should be included in the record. Depending on the level at which a repository tracks deletions, a header with a "deleted" value for the status attribute may be returned, in case the metadata format specified by the metadataPrefix is no longer available from the repository or from the specified item.

• There was a request q, to which this XML document (r) is a response.
• The request q raised no error and no exception.
• The item requested (i) exists within the repository (a).
• The metadata format requested exists (or did exist) for item i.
• ...

request_verb(q, ‘GetRecord’)

∧ errorfree(q)

∧ item_isin_repository(i, a)

∧ repository_hasformat_foritem(a, format-id, i)

∧ ...

• S: list of inferences in source
• T: list of inferences in target
• ‘ST mapping rules’: crosswalk from source concepts to target concepts. E.g.

  (s_olist(x) ∨ s_ulist(x) ∨ s_deflist(x)) ⇒ t_list(x)

• ‘TS mapping rules’: crosswalk from target concepts to source concepts. E.g.

  t_list(x) ⇒ (s_olist(x) ∨ s_ulist(x) ∨ s_deflist(x))

Does this follow from T?

Does this follow from S?

• noise-free
• non-lossy

• prove procedure correct
• prove correct for one particular document
• testing during development

I remember when "proving software correct" was an interesting topic, but it has not shown itself to be of much use in the long run.

• Not all digital objects are XML.
• Not all information should be preserved.
  • character-encoding
  • HTTP-equivalent (and other metadata?)
  • ...
• Different levels of detail (refinement, abstraction).
• Different ways of carving the world (sloppy overlap).

• Allow sliding scale of generality.
  (author, editor, translator, composer, arranger — but also creator)
• Allow open-ended annotation (e.g. for problems).
• Provide documentation.
• Provide complete documentation.