* Schemantic Web version 0.0 (beta)                     -*- outline -*-

This is the Schemantic Web, a collection of tools related to the
Semantic Web for portable Scheme.

This file is written by Taylor R. Campbell and placed in the Public
Domain.  All warranties are disclaimed.

This library contains

- a URI abstraction;
- an RDF node abstraction;
- an RDF graph abstraction, with two different implementations;
- a minimal HTTP 1.0 client;
- a SPARQL query generator;
- a SPARQL-over-HTTP client;
- an RDF N-Triples parser; and
- an RDF Turtle parser.

The URI abstraction is mostly interface-compatible with the one found
in MIT Scheme, written by Chris Hanson.  However, it is written in
portable Scheme, and does not rely on MIT Scheme's parser language.

This code relies on Taylor R. Campbell's Parscheme library, a
collection of tools for writing parsers in Scheme.  It is available at
<http://mumble.net/~campbell/scheme/parscheme.tar.gz>, or by Darcs at
<http://mumble.net/~campbell/darcs/parscheme/>.

This code is lightly tested, in test suites found in files named
`test-*.scm', supplied with data in the `tests/' subdirectory.  There
is no documentation, yet, but there are some minimal examples beyond
the test suites in the `examples/' subdirectory.

The Schemantic Web can be loaded into the following Scheme systems:

- Scheme48:

  Load the following files into the config package:

    aux/s48-interfaces.scm
    aux/s48-packages.scm
    s48-interfaces.scm
    s48-packages.scm

** Portability

At present, this code runs only in Scheme48, but because it is written
in a portable manner, porting it to other Schemes should be easy.
Although the code relies on some non-standard extensions, these have
all been very carefully isolated, and most of the non-R5RS dependencies
are SRFIs.  In particular, this collection uses

  SRFI 1 (List Library),
  SRFI 6 (Basic String Ports) with the following utility:

    (define (call-with-string-output-port receiver)
      (let ((output-port (open-output-string)))
        (receiver output-port)
        (get-output-string output-port))),

  SRFI 9 (Defining Record Types),
  SRFI 13 (String Library),
  SRFI 14 (Character-Set Library),
  SRFI 23 (Error Reporting Mechanism), and
  SRFI 45 (Primitives for Expressing Iterative Lazy Algorithms),

all of which except for SRFI 45 are widely supported.  SRFI 45 is not
an onerous burden, however; it would suffice to define

  (define-syntax lazy
    (syntax-rules ()
      ((LAZY promise)
       (DELAY (FORCE promise))))),

if space safety is not a concern.  If space safety is a concern, then
the SRFI 45 reference implementation is available.

The only other non-standard extensions are

- procedures to convert US-ASCII characters to and from their US-ASCII
  codes (CHAR->ASCII and ASCII->CHAR), which in many systems can be
  defined as aliases for CHAR->INTEGER and INTEGER->CHAR; and
- hash tables that are keyed by strings and that hold the associated
  data only weakly, for interning URIs and URI authorities (`internment
  camps': (MAKE-STRING-INTERNMENT-CAMP), (INTERN <internment-camp>
  <string-key> <datum-generator>), (SOFT-INTERN <internment-camp>
  <string-key>); see packages.scm for an example definition).

Finally, the simple HTTP client requires networking support, which is
highly dependent on the implementation.  Consequently, it is at present
implemented for Scheme48 specifically in s48-http-client.scm, but
implementing it in other Scheme systems is relatively straightforward.
Also, one of the RDF graph implementations uses a mapping abstraction,
which in Scheme48 is implemented using hash tables in s48-rdf-map.scm.
This, too, is straightforward to implement alternatively.

** Documentation

To be written.