NAME
    *Load.pm* -- load data into Qios database.

DESCRIPTION
    Module *Load.pm* includes the functions for loading XML data, conversion
    of the DTD schemata into internal database schemata, and re-engineering
    of the database schemata from XML data.

Schema discovery
    The method for the re-engineering of the schema from the data is
    implemented. It tends to group the information to construct the
    object-relational schema (objects which besides scalar-valued attributes
    include also multi-valued attributes ranging over scalars or objects)
    rooted around the top-level data elements. The types of elements are
    computed by determining the least general type that covers all
    instances.

    Two parameters by which the creation of the object-relational schemata
    can be controlled in schema re-discovery and in DTD load process are as
    follows. The boolean parameter *collsvd* controls the collapse of the
    function elements into the subsuming relation. By turning the option
    *collsvd* on, all the single-valued elements (including a single data
    entry) are included in the upper-level relational schema. Similarly, the
    boolean parameter *collmvd* controls the collapse of relations including
    a single multi-valued attribute modeling thus sequences of simple
    elements including a single data entry. The parameters are accessible
    thru the database environment using the command *set*.

XML
    *Qios* includes the method for the translation of the DTD schemata into
    the internal database format. Similarly as the procedure for
    re-engineering the schema from the XML data, the procedure for the
    translation of DTD schemata into internal format constructs
    object-relational schemata. User can control the conversion of the
    functional and multi-valued path expressions---they can be either
    collapsed into single or multi-valued attributes, or retained. Same as
    by the procedure for the re-engineering of the object-relational
    schemata from the XML data, the conversion of DTD can be controlled
    using system parameters *collsvd* and *collmvd*.

    The basic rules for the translation of DTD files into object-relational
    schemata are as follows. XML attributes are converted into functional
    (relational) attributes describing the relation of the host element. The
    elements described with more than one components (elements) and
    attributes are converted into relations. The creation of the relations
    for the attributes including a single data entry (XML attribute or
    component element) is controlled by the parameters *collsvd* and
    *collmvd* described in the previous section.

Data loader
    The method for loading XML data into the internal database follows
    strictly the structure of the data defined by the database schemata (ie.
    the set of class objects) to unravel on-the-fly the structure of the XML
    records. The method tends not to use the parameters described above for
    the decisions during the loading process.

COMMENTS
    This module is part of the *qios* programming environment.