VHDL Issue Number:      0113
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                Scope of expanded names is unclear.
Related Issues:         None.
Relevant LRM Sections:  6.3, 10.1, 10.3
Key Words and Phrases:  Expanded names, selected names, declarative regions,
                        secondary units
Current Status:         ISAC-Approved
1076-1993 Disposition:  Superseded (ISAC Issues Outstanding)
Disposition Rationale:  
Superseded By:          1057
-----------------------
Date Submitted:         1988/07/07
Author of Submission:   Paul Menchini
Author's Affiliation:   CAD Language Systems, Inc.
Author's Post Address:  P.O. Box 13036
                        Research Triangle Park, NC  27709-3036
Author's Phone Number:  (919) 361-1913
Author's Fax Number:    
Author's Net Address:   mench@clsi.com
-----------------------
Date Analyzed:          1991/01/22
Author of Analysis:     Doug Dunlop
Revision Number:        $Revision: 1.9 $
Date Last Revised:      $Date: 1995/05/13 19:34:42 $


Description of Problem
----------------------
It is unclear where certain expanded names are legal.  To illustrate, consider
the following design units:

        entity E is
          port (P: in bit);
        end E;

        architecture A of E is
          signal Q: bit;
        begin
          ... E.P ...;  -- which of these expanded names are legal?
          ... A.Q ...;
          ... E.Q ...;
          ... A.P ...;
        end A;

The LRM makes two different, but similar, statements regarding expanded names.
The first, in Section 6.3, states:

        "An expanded name denotes an entity declared immediately
         within a named construct if the prefix denotes a construct
         that is an entity, an architecture, ..., and the suffix is
         the simple name, character literal, or operator symbol of
         an entity whose declaration occurs immediately within that
         construct.  This form of expanded name is only allowed
         within the construct itself."

Using a strict interpretation, the name E.Q is not legal because Q is
not declared within the named construct E.  Also the name A.P is not
legal because the declaration of P is not within A.

However, consider the following statement, in Section 10.3, page 10-4 of the
LRM:

        "Finally, within the declarative region associated with a
         construct other than a record type declaration, any
         declaration that occurs immediately within the region is
         visible by selection at the place of the suffix of an
         expanded name whose prefix denotes the construct."

However, the legality of the names is not obvious because the entity
declaration together with the architecture body form a single declarative
region (Section 10.1). How is the declarative region denoted?  Can either E or
A denote the entire region or does each denote a part of it?

I have been informed by the language designers that the intent was for at least
E.P and A.Q to be legal.


Proposed Resolution
-------------------
Allow only E.P and A.Q in the above example to be valid.


VASG-ISAC Analysis & Rationale
------------------------------
The language problem described above is genuine.

The quoted sentence from LRM 6.3 seems to be the defining rule for expanded
names and seems relatively clear.  The sentence makes use of the terms
"construct" and not "declarative region".  The problem sentence is the one
quoted from LRM 10.3 since it does not deal with the case where multiple
"constructs" or associated with a declarative region.  It seems to the ISAC
that the most natural interpretation here is to require the entity name
prefix for those items declared within the entity and the architecture 
name prefix for those items declared within the architecture body.  This
interpretation matches the proposed resolution given above.


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
The use of an expanded name to reference an item declared immediately within
an entity declaration must use the entity name as a prefix.  Similarly, the
use of an expanded name to reference an item declared immediately within
an architecture body must use the architecture name as a prefix.


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
Revise the quoted sentence from LRM 10.3 to reflect this interpretation.