XML input format

The XML input format can be used everywhere where the text-based format is used. Currently, it requires oofem to be compiled with -DUSE_XML=1, which will links against system-installed pugixml library for parsing XML. XML input will be activated for input files having the .xml extension automatically.

• records (lines in the text input) are expressed as entities, fields are entity attributes;

• entities are nested;

• text between elements (PCDATA as it is called in XML) is only used for <Output>...</Output> and <Description>...</Description> (not anywhere else);

• there is an experimental tool to convert from text to XML which currently passes (almost) all unit tests; that repository also contains all tests converted to XML;

• tags and attributes are case-insensitive, but message (warning) will be shown for non-matching case;

• special characters in field names are replaced by _ to conform with XML attribute names (thus f(t) becomes f_t_, a/c becomes a_c)

• the _ attribute denotes object to be created, e.g. <Analysis _="StaticStructural"> (keyword argument in the text format)

In comparison to the text format:

• XML is machine readable and writeable, using usual XML tools;

• versioned (<oofem version="...">), with automated upgrade paths (not yet implemented);

• number of enumerated sub-itmes (such as nelem in a domain) are inferred (the Components size record is therefore completely missing);

• ordering of heterogeneous records (such as whether <Sets> are specified before <Elements>) is arbitrary;

• id’s of enumerated elements are optional (but checked);

• XML comments <!-- .... --> are supported;

• XML fragments can be included via <xi:include href="other.xml">;

• #%BEGIN_CHECK% ... #%END_CHECK% (ErrorCheckingExportModule) is specified as XML, using <ErrorCheck> group, instead of special syntax.

Field formats

Since attributes in XML are string-only, here we describe how other types are represented:

type	description	notes
integers, floats	usual ASCII representation
flags	attributes without value are written as attribute="" in XML	non-empty value will produce warning about not having been processed
boolean	true (1, y, Y and a few others), false (0, n, N and others)	unrecognized value produces error
1D arrays (ints, floats)	space-separated
2D matrices	colon-separated rows, space-separated elements	e.g. a11 a21; a12 a22
dictionaries	colon-separated items, space-separated key and value	e.g key1 value; key2 value
ranges	comma-separated items or contiguous ranges with dash (minus)	e.g. 1-4,7,9-11; as alternative: 1..4,7,9..1
enums	specified as number of keyword

Input example

• spring01.xml:

  <oofem version="2">
    <Description>Patch test of 1D spring element along x axis</Description>
    <Analysis _="StaticStructural" nsteps="1" />
    <Domain domain="1dtruss">
      <OutputManager tstep_all="" dofman_all="" element_all="" />
      <Nodes>
        <Node id="1" coords="0. 0. 0."  />
        <Node id="2" coords="0. 0. 0."/>
      </Nodes>
      <Elements>
        <Spring nodes="2 1 2" crosssect="1" mode="0" k="2.0"/>
      </Elements>
      <CrossSections>
        <SimpleCS thick="0.1" width="1.0" material="1" set="1"/>
      </CrossSections>
      <Materials>
        <dummymat />
      </Materials>
      <BoundaryConditions>
        <BoundaryCondition id="1" loadtimefunction="1" dofs="1" values="0.0" set="2"/>
        <NodalLoad id="2" loadtimefunction="1" dofs="1" components="1.0" set="3"/>
      </BoundaryConditions>
      <InitialConditions/>
      <LoadTimeFunctions>
        <ConstantFunction f_t_="1.0"/>
      </LoadTimeFunctions>
      <Sets>
        <Set nodes="1"/>
        <Set nodes="1"/>
        <Set id="3" nodes="2"/>
      </Sets>
    </Domain>
    <xi:include href="spring01-exportmodules.fragment.xml" />
    <!--
      this is what is indirectly included (as xi:include test)
      <ExportModules>
        <errorcheck tolerance="1e-4">
          <NODE tStep="1" number="2" dof="1" unknown="d" value="0.5"/>
          <REACTION tStep="1" number="1" dof="1" value="-1"/>
        </errorcheck>
      </ExportModules>
    -->
  </oofem>
  

• spring01-exportmodules.fragment.xml, pulled into the file above via xi:include:

  <ExportModules>
      <xi:include href="spring01-errorcheck.fragment.xml" />
  </ExportModules>
  

• spring01-errorcheck.fragment.xml, pulled in indirectly — the fragment above includes it in turn:

  <errorcheck tolerance="1e-4">
      <!-- check nodal displacements -->
      <NODE tStep="1" number="2" dof="1" unknown="d" value="0.5"/>
      <!-- element stresses and strains -->
      <!-- <ELEMENT tStep="1" number="1" gp="1" keyword="1" component="1" value="1.0"/> -->
      <REACTION tStep="1" number="1" dof="1" value="-1"/>
  </errorcheck>