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<Paper uid="P05-3028">
  <Title>A Flexible Stand-Off Data Model with Query Language for Multi-Level Annotation</Title>
  <Section position="6" start_page="111" end_page="111" type="relat">
    <SectionTitle>
4 Related Work
</SectionTitle>
    <Paragraph position="0"> In the EMU speech database system (Cassidy &amp; Harrington, 2001) the hierarchical relation between levels has to be made explicit. Sequential and hierarchical relations can be queried like with simplified MMAXQL, with the difference that e.g. for sequential queries, the elements involved must come from the same level. Also, the result of a hierarchical query always only contains either the parent or child element. The EMU data model supports an association relation (similar to our markable pointer) which can be queried using a =&gt; operator.</Paragraph>
    <Paragraph position="1"> Annotation Graphs (Bird &amp; Liberman, 2001) identify elements on various levels as arcs connecting two points on a time scale shared by all levels. Relations between elements are thus also represented implicitly. The model can also express a 9A means to express distance in terms of markables is not yet available, cf. Section 5.</Paragraph>
    <Paragraph position="2"> binary association relation. The associated Annotation Graph query language (Bird et al., 2000) is very explicit, which makes it powerful but at the same time possibly too demanding for naive users.</Paragraph>
    <Paragraph position="3"> The NITE XML toolkit (Carletta et al., 2003) defines a data model that is close to our model, although it allows to express hierarchical relations explicitly. The model supports a labelled pointer relation which can express one-to-many associations.</Paragraph>
    <Paragraph position="4"> The associated query language NXT Search (Heid et al., 2004) is a powerful declarative language for querying diverse relations (incl. pointers), supporting quantification and constructs like forall and exists.</Paragraph>
  </Section>
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