This directory contains source code defining a collection of
application independent classes that includes a common "base" class
for all entity class definitions as well as classes for maintaining
meta-information about schemas in the schema class library.  These
core classes are also used by the editor and probe-ui libraries.  The
core classes use a common set of virtual functions for reading and
writing to exchange files, reading and writing user interface formats,
and validating their data.

Directory Contents:

sdaiEnum.cc, sdaiEnum.h
Defines SdaiEenumeration (previous STEPenumeration), an abstract base
class, and derived classes Logical and Boolean which inherit from
SdaiEnumeration.  Logical and Boolean model the LOGICAL and BOOLEAN
types in EXPRESS.  Other enumerated types can be implemented by
subclassing SdaiEnumeration.

ExpDict.cc, ExpDict.h, ExpDict.inline.cc
Defines classes representing descriptors for EXPRESS schemas,
entities, attributes, and types.  Instances of these classes comprise
a dictionary to the contents of an application model's schema.  The
instances populate a Registry object (see Registry below).

Registry.h, Registry.inline.cc
Defines Registry, a class with three data members: a hash table of
active schemas, a hash table of active types, and a hash table of
entity instances.  The Registry object serves as a dictionary to the
contents of an application model's schema.  It is also used to create
new entity instances.

STEPaggregate.cc, STEPaggregate.h
Defines a collection of abstract classes for representing aggregations
of simple types, enumerations, selects, and entity types.  The
following subclasses of STEPaggregate are stubs and have yet to be
implemented: Array, Bag, Set, List.  Defines RealAggregate, an
abstract subclass of STEPaggregate for implementing aggregations of
real numbers.

STEPattribute.cc, STEPattribute.h, STEPattribute.inline.cc
Defines STEPattribute, an element in a STEPentity's list of attributes.

STEPattributeList.cc, STEPattributeList.h
Defines the class STEPattributeList -- a list of pointers to 
STEPattribute objects.  The nodes on the list point to STEPattributes.
STEPattributeList is derived from SingleLinkList.

sdaiSelect.cc, sdaiSelect.h
Defines SdaiSelect, an abstract base class implementing the EXPRESS 
SELECT data type.  

sdaiString.cc, sdaiString.h
Defines SdaiString, a class implementing the EXPRESS STRING data type.

STEPundefined.cc, STEPundefined.h
Defines SCLundefined, a class for implementing any types not defined
in other SCL classes.  

sdaiBinary.cc, sdaiBinary.h
Defines SdaiBinary, a class implementing the EXPRESS BINARY date type.

SingleLinkList.cc, SingleLinkList.h, SingleLinkList.inline.cc
Defines the classes SingleLinkList and SingleLinkNode, implementing a
generic singly linked list.  These two classes are both abstract base
classes.

baseType.h
Defines BASE_TYPE, an enumeration of the base data types in EXPRESS.

read_func.cc, read_func.h
Defines a collection of functions for reading and validating
numerical data.

sdai.h
This file is basically a bunch of #include statements for all of the
header files corresponding to the specifications in Annex D of Part 22
(the proposaed SDAI/C++ language binding).  Defines STEPentity, the
abstract base class of all generated entity classes.
