XLIST

A generic container. It can be used to construct most of the common container classes (although these can only be validated at postprocessing time). The DTD imposes very little constraints on how XLIST can be used, but CONTENT can be set to show certain common methods. XLIST can contain any or all of the common generic data items (A, ARRAY, XVAR and XLIST itself). The commonest uses are:

• CONTENT=STRUCT (default). The XLIST can contain any variety of components (similar to a struct in C. The STRUCT can be given a name with the STRUCT= attribute which could be used, for example, to define a PERSON (age, name, etc). SGML cannot parse the validity of such a STRUCT which must be done by the postprocessor. By convention it will impose no restricions, but if the user wishes to define bags, sets, etc. they can do this with the STRUCT= attribute.

  Example:
  <XLIST STRUCT=PERSON><XVAR>John Doe<A HREF=jdoe@xyzzy.com></A></XLIST>

• CONTENT=ARRAY. A Homogeneous array of other components. Examples:
  • A list of dates:
    <XLIST CONTENT=ARRAY SIZE=3 SUBELEMENT="XVAR">
    <XVAR TYPE=date>1995-06-03</XVAR;>
    <XVAR;>1995-06-07</XVAR;>
    <XVAR;>1995-06-08</XVAR;>
    </XLIST>
  • A list of pointers:
    <XLIST CONTENT=ARRAY SIZE=3 SUBELEMENT=HREF>
    <A HREF=alpha></A>
    <A HREF=beta></A>
    ;</XLIST>
    
• CONTENT=BIBLIST. A list of BIBs (citations).
• CONTENT=GRAPH. A special case of CONTENT=TABLE primarily designed to be displayed graphically. The ARRAY can have BUILTINs of 1 XAXIS and 1+ YAXIS. There may be additional hints to suggest axis scales, directions, etc. through the DISPLAY attribute. Not fully worked out yet.
• CONTENT=NODE. This designates the XLIST as a node in a tree. All contained XLISTs are assumed to be potential child nodes. Other contained objects belong to the node. If a contained XLIST is not a NODE, it is treated as belonging to the node like the other objects, and will not be recursively explored by a tree search algorithm. (It might be a STRUCT, for example). Example:
  <XLIST CONTENT=NODE TITLE=vertebrate>
  <XLIST CONTENT=NODE TITLE=mammal>
  <XVAR>Suckles its young</XVAR>
  <XLIST CONTENT=NODE TITLE=human>
  <XVAR>Walks</XVAR></XLIST>
  <XLIST CONTENT=NODE TITLE=bat>
  <XVAR>Flies</XVAR></XLIST>
  </XLIST>
  <XLIST CONTENT=NODE TITLE=reptile>
  <XVAR>Lays eggs</XVAR>
  <XLIST CONTENT=NODE TITLE=snake>
  <XVAR>Slithers</XVAR></XLIST>
  <XLIST CONTENT=NODE TITLE=crocodile>
  <XVAR>Swims</XVAR></XLIST>
  </XLIST>
  </XLIST>
  
• CONTENT=TABLE. This represents a (rectangular) (relational) table, based on columns. The columns can be of two sorts, XVAR or XLIST, and all columns must have the same length. One or more ARRAY columns can be designated as KEYs (using the KEY attribute) - the XLIST columns cannot be used as KEYs. Example:
  <XLIST CONTENT=TABLE SIZE=3>
  <ARRAY CONTENT=INTEGER TITLE="Age" UNITS=year>23 37</ARRAY>
  <ARRAY KEY=PRIMARY TITLE="Name">"John Doe" "Jane Doe"</ARRAY>
  <XLIST CONTENT=ARRAY TITLE="WWW">
  <A HREF="john"></A>
  <A HREF="jane"></A></XLIST>
  </XLIST>
  

  The format of the table is different from the HTML 2.1 tables, (TAB) and even when that comes in, XLIST will be retained. It has much more possibility for semantics.

Note that the counts (COLUMNS, ROWS, SIZE) are advisory and primarily used for checking. The postprocessor is assumed to be able to count.

Content Model

Because XLIST can be used in so many ways the possible content is completely flexible and I have used the SGML keyword ANY. Any element in any of the DTDs (including #PCDATA) can be used and in any order. Note that CONTENT=TABLE and CONTENT=GRAPH put strong constraints on the contained sublements.

Content

• ANY

ATTRIBUTES
CONTENT DECLARATION

Tag Minimization

Open Tag: REQUIRED
Close Tag: REQUIRED

Parent Elements

• admin -- Administrivia.
• atoms -- A generic container for atomic coordinates and properties
• bonds -- A generic container for bonds and their properties
• cml -- A toplevel DTD encompassing HTML 2.0, TecML and MOL.
• cryst -- Crystallographic data, especially unit cell and symmetry.
• feature -- Features of macromolecules (e.g. SITE, MUTATION).
• formula -- Chemical formula.
• mol -- Toplevel container for molecular information.
• reaction
• relation -- Describes relationship between objects, including hyperlinks. Experimental at present.
• sequence -- Represents a macromolecular sequence.
• symmetry -- Molecular symmetry.
• tecml -- A toplevel container for the TecML DTD.

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