xml basic principles


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Basic Principles

The ArcSDE XML API provides support for storing XML documents in a database and allows for searching data stored in the documents, such as ArcGIS metadata.

XML column

The XML column represents a column in an ArcSDE table, similar to spatial or raster columns, and contains references to associated XML data, which is stored in several internal tables. These internal tables are created and managed by ArcSDE. They store associated XML data such as indexes, tags, and documents. The XML database schema shows an XML column's association with these internal tables.

In the Java API, the XML column is represented by the SeXmlColumn class, while the C API provides several functions (SE_xml*). more ...

XML index and tags

ArcSDE supports two indexing concepts:

Index templates: These define all location paths and data types in a particular schema.
Index definitions: These define which location paths are to be indexed for a particular XML column.

An XML index can have three types of tags:

SE_XML_INDEX_DOUBLE_TYPE: Used for all numeric tags.
SE_XML_INDEX_STRING_TYPE: Used for all string tags.
SE_XML_INDEX_VARCHAR_TYPE: Used for all text (simple strings) tags.

Search on XML columns can be tag-based (xpath) or full text search. A tag-based search uses the tags to search the XML documents. An index is used to enable searches on XML columns. An XML column can have two types of indexes to support different types of text searches.

• Text index:
o A text index associated with the XML document supports full text searches against all content in the XML document. The XML tags in the document are transparent to the text index. In other words, the text index is created in the database on the content with all XML markup removed, thus allowing quick and efficient text searches on the document.
o A text index associated with the XML tag (SE_XML_INDEX_STRING_TYPE) supports tags-based (xpath) searches in the XML document.

• BTREE index: Full text indexes, apart from being bigger and slower than BTREE indexes, are updated outside the transaction scope, which is inefficient when used to index feature property sets. Further, full text indexes are not available on all databases. To overcome the limitation of full text indexes, the tag-indexing model has been extended in ArcSDE 9.2 to include Numbers, Strings, and Text. Text tags (simple strings) would now be indexed using a BTREE, while string tag uses the full text indexer.

Search on XML columns can either be tag-based (XPATH) or full text search. A tag-based search uses tags to search the XML documents. An index is used to enable searches on XML columns. An XML column can have three types of text indexes to support different types of searches.

Text index: A text index associated with the XML document supports full text searches against all content in the XML document. The XML tags in the document are transparent to the text index. In other words, the text index is created in the database on the content with all XML markup removed, thus allowing quick and efficient text searches on the document.
BTREE index: Full text indexes, apart from being bigger and slower than BTREE indexes, are updated outside the transaction scope, which is inefficient when used to index feature property sets. Further, full text indexes are not available on all databases. To overcome the limitation of full text indexes, the tag-indexing model has been extended in ArcSDE 9.2 to include Numbers, Strings, and Text. Thus, simple strings would now be indexed using a BTREE, while string tags will use the full text indexer. more ...

XPATH Searches

An index associated with specific XML elements supports searching text or numeric data in those elements. This index is associated with the SDE_XML_INDEXES table. As an example of using an XPATH index, the user might search only the content in an XML element containing scale information to find GIS resources that are appropriate for the user's application.

A tag or XPATH index on an XML column is an optional index. It contains a list all tags and their data types and lets people search the content of that specific XML element or attribute in each document. It can be created manually, or based on an ArcSDE analysis of some sample documents, or based on a set of templates.

XML Document

An XML document is a hierarchically structured text document consisting of labels, called tags, and data. It is used for storing and retrieving XML documents in ArcSDE.

The ArcSDE API uses the XML Document object (SeXmlDoc in Java, SE_xml_doc* functions in C) to store and retrieve an XML document from ArcSDE. ArcSDE Insert and Query stream objects communicate with the XML Doc object, which in turn is associated with the XML column. more ...