Re: The OverRelational Manifesto. VOCIFEROUS IGNORANCE vs. NUMB DOGMA.(the sequel)
> Do you mean by "object's component" a field?
It can be field. Commonly I mean something what contains (or returns)
value. So it can be fields, attribute, method - anything what define in
specification of object type to have value what describe these object.
There are two king of types in RxO system - object types and valued
types.
"...In the general case, the specification of an object type includes
1. the type name;
2. a list of parent types (unless otherwise is defined explicitly,
the
parent type is the Object type implicitly);
3. a collection of specifications of components, which include (a)
the
component name; (b) the value type of the component, and (c),
optionally, the set of parameters each one described as a pair
<parameter name, value type of the parameter>;
4. a set of data integrity constraints, i.e., keys...."
...where "...The value types are the following:
1. scalar type including the basic ones (numerical, symbolic,
Boolean,
etc.) and reference types.
2. constructed tuple type. A value of this type (hereinafter, a
tuple)
is a set of pairs "an attribute name, a value of the attribute of the
scalar type." Accordingly, the tuple type is defined as a set of
pairs "attribute name, scalar type of the attribute."
3. constructed set type. A value of this type (hereinafter, a set)
is a
set of scalar or tuple values. Accordingly, a set-type variable is
defined as (variable_name AS SET OF name_of_scalar_or_tuple_type)..."
When these types are specified and implemented, then we can create both
the objects and global variables of valued types. As you can see SET
types is constructed types which are defined as set of tuples, where
each typle is set of scalars. You can consruct this type as you wish -
directly in object type specification or somewhere else.
>If so then nothing prevents me from having an explicit declaration of
>all relations and then using set-valued attributes via "SET OF" keyword,
>for example:
>
> MyType {
> INT myIdentifer;
> DOUBLE balance;
>} CONSTARIN myIdentifer Key
>
>and then we write
>
>SHIPMENT {
> ...
> Items SET OF MyType;
> ...
Is "MyType" a relation definition? In this case you shouldn't use "SET
OF" when you describe "Item"? because result of such definition is set
of relations(I cannot imagine what is it:) ) - not single relation. But
if "MyType" is just tuple definition you cannot define keys into
definition expression, because there is no yet set of tuples here. So
you can write
MyType {
myIdentifer INT;
balance DOUBLE;
}
ObjectType2 {
...
SetValuedField SET OF MyType CONSTARIN myIdentifer Key;
...
}
Or you can write something like
CREATE RelationType MyType {
myIdentifer INT;
balance DOUBLE;
} CONSTARIN myIdentifer Key
ObjectType2 {
...
SetValuedField MyType;
...
}
In any cases you can use "MyType" repeatedly. Why not?
RxO system works with something, what is more complex than single
relation. The only thing exists in RDM what is more complex than single
relations - is is set of relations. But each of these relations is
usual relation as it is defined in RDM and each relation can be defined
in any way if the result of this definition is true relation.
Received on Mon May 29 2006 - 14:29:50 CEST
Original text of this message
