Understanding the NCML Handler

The NCML handler has 53 classes. The classes fall into four broad categories:

Utilities

Used to perform various routine tasks (namespace agg_util)

BES Framework

Used to instantiate the module and provide interface hooks for the BES DAP module (namespace ncml_module)

NCML Parser

A SAX2 parser that uses the NCML text to build one or more DAP objects (DDS, DataDDS, etc.) (namespace ncml_module)

AIS code

Classes that add, modify or remove variables and attributes. (namespace ncml_module)

Aggregation code

Classes that build Join New and Join Existing aggregations (namespace ncml_module)

The following sections list the classes/files that fall into these five categories along with some notes about those classes where appropriate.

In the listing of classes, indentation is used to show parent-child relationships within the module. For classes that inherit from BES framework or libdap classes, child: public parent is used.

BES Framework

1. NCMLModule: public BESAbstractModule
2. NCMLRequestHandler: public BESRequestHandler
3. NCMLContainer: public BESContainer
4. NCMLContainerStorage: public BESContainerStorageVolatile

NCML Parser

The classes the make up the core of the SAX2 parser are:

1. SaxParser
   1. SimpleLocationParser
2. SimpleTimeParser
3. XMLHelper
4. SaxParserWrapper

Those classes are augmented by the Element classes that are used to build the in-memory objects the NCML needs to carry out the AIS or Aggregation tasks specified by a given NCML file. They are:

1. NCMLElement
   1. AggregationElement
   2. AttributeElement
   3. DimensionElement
   4. ExplicitElement
   5. NetcdfElement
   6. ReadMetadataElement
   7. RemoveElement
   8. ValuesElement
   9. ScanElement
   10. VariableElement
   11. VariableAggElement