# RE: Questions about "equal" fundamental facet

From: <sandygao@ca.ibm.com>
Date: Thu, 25 Apr 2002 11:37:09 -0400
To: "Ashok Malhotra" <ashokma@microsoft.com>

Message-ID: <OF740C2B83.04F41778-ON85256BA6.004E22E1@torolab.ibm.com>
```Hi Ashok. Thanks for your reply.

> [AM] I don't know how to tell if two value spaces are subsets of some
primitive value space.  I only know such a relation exists for types
derived by restriction.

There are 19 primitive types. If hexBinary and base64Binary share the same
value space (this seems to be true according to how their value spaces are
defined); QName and NOTATION share the same value space; float has a value
space that's a subset of that of double, then we have 16 primitive value
spaces. We need another one for list values: list of a union of the other
16 primitive value spaces. So we have totally 17. Each value space
represents its values in a distinct way, that is, a different Java class if
it's represented in Java.

Now given two values, no matter how they were generated, by which types,
their equality can be checked independent of the types:

The two values are equal if and only if they both belong to the same
primitive value space (call it PVS) (that is, both are list values, or both
are non-list values, and belong to the same non-list primitive value
space), and the appropriate case among the following is true:
1.1 the PVS is not the list value space, and the two values represent the
same value in this PVS.
1.2 the PVS is a the list value space, and the two values have the same
length, and all their item values at matching index are equal.

IMO, users would prefer this over type-based equality, because it allows
float(1.0) == double(1.0); int(1) == unsignedInt(1); etc.

There is one point worth thinking about though: what's the value space of
"anySimpleType"?

Places of the spec indicate that it's the union of the value spaces of all
primitive types, but I always have difficulties accepting it. The reason is
that anySimpleType doesn't have the ability to understand a lexical
representation, and convert it to an actual value. For example, if we have
the lexical value "1.0", different primitive types know whether it's valid,
and how to interpret it, but anySimpleType doesn't. So it's value space
should really be an empty set (or at most the value space of "string" type,
but I don't like it). This seems to violate the "derivation constraints
value space" rule. But since we already made some exceptions for primitive
types deriving from anySimpleType, it won't hurt to have one more.

BTW, it'd be appreciated if someone could answer my other questions:
1. what are the values of totalDigits/fractionDigits for decimal "0.00"?
2. Whether international decimal characters that are out of the range
#x30~#x39 (#x660, for example) are allowed in date time types?

Thanks,
Sandy Gao
(1-905) 413-3255
sandygao@ca.ibm.com

"Ashok
<ashokma@micro       cc:
soft.com>            Subject:     RE: Questions about "equal" fundamental facet

04/24/2002
04:59 PM
to "Ashok
Malhotra"

All the best, Ashok

===========================================================

-----Original Message-----
From: sandygao@ca.ibm.com [mailto:sandygao@ca.ibm.com]
Sent: Wednesday, April 24, 2002 11:43 AM
Subject: Questions about "equal" fundamental facet

1. Is it defined on "value spaces", or "types"?

In 4.2.1 of the datatype spec: "Every ·value space· supports the notion of

equality, ...". So it seems that "equal" is defined on "value spaces". Does

this imply that two (unconnected) types (with the same value space) can

have equal values? For example, hexBinary and base64Binary have the same

value space ("the set of finite-length sequences of binary octets").

hexBinary value "00" and base64Binary value "AA==" both represent one byte

of value "0". Then are the two values equal? I would say they are equal, if

"equal" is defined on value spaces.

But 3.11.1 of the structure spec says "Values of differing type can only be

equal if one type is derived from the other, and the value is in the value

space of both". Here it seems to indicate something different. Is this a

[AM] Equality is defined on values.  The values must be in the same value
space. Since derivation by restriction merely narrows the value space a
value of a base type may equal a value of a derived (by restriction) type.

2. Does the types have to be related by ·restriction· or ·union·?

If type A restricts "integer" by setting "minInclusive=0", and B restricts

"integer" by setting "maxInclusive=10". Now A and B are not related by

restriction or union. But I still expect value "5" from both types (values

spaces) to be equal.

(If they have to be related by ·restriction· or ·union·, doesn't 3.11.1 of

the structure spec need to be modified to be more strict, instead of simply

saying "derived from"?)

[AM] By restriction.

My take on these 2 questions:

1. "equal" should be defined on value spaces, because equal values are

equal, no matter how they were lexically represented.

[AM] Correct!

2. Types used to generate equal (actual) values don't need to be related.

As long as there exist a (primitive) value space to which both values

belong, and the two values are equal in that value space, then they are

equal. This means hexBinary and base64Binary can generate equal values, so

can QName and NOTATION. Further on this, maybe the value space of "float"

should (or already is) be a subset of that of "double", so that these types

can generate equal values.

[AM] I don't know how to tell if two value spaces are subsets of some
primitive value space.  I only know such a relation exists for types
derived by restriction.

Thanks,

Sandy Gao