ERL is an XML-based language that describes entity-relationship schemata enriched with information that is useful in reification and interface construction. It is the foundation over which ERW is built. To understand ERL, you must also understand how ERtool will reify ERL-defined entity-relationship schemata.
Before giving the reference to ERL elements, it is useful to have an informal discussion of what you can describe in ERL.
ERL documents are made of an
element, that can contain
(describing entity types) and
elements (describing relationship types). Additionally, the
enum element can be used to create
static enumerative types (attributes of this type
can assume a finite and fixed number of values), and the
fset element can be used to create
fileset types (fileset attributes associate to an
entity a set of files with attributes).
ent element there are
attr elements, describing attributes,
isa elements, describing
attr element has some
XML attributes that let you specify the type of the attribute
and whether it is mandatory (that is, whether the user must provide some
input for that attribute).
rel element you can find,
attr elements, but you will
certainly find two
leg elements, which
specify the first and second leg of a multirelation (including the source
entity, the target entity and cardinality constraints).
All elements let you insert optional text inside them; it will be added to the documentation.
Unfortunately, the word "attributes" has different meanings in the XML and entity-relationship world.