Re: MSC-News: Conditions in HMSC

Subject: Re: MSC-News: Conditions in HMSC
From: Michel Reniers (
Date: Fri Jan 23 1998 - 14:57:52 GMT

The originator of this message is responsible for its content.
-----From Michel Reniers <> to mscnews -----

Oystein Haugen wrote:
> Dear Jan, Dagbjorn and other HMSC fans
> It seems that Dagbjorn, Jan and I agree on the desirability to allow
> fragments without start/end symbols in HMSC, but Jan and I have
> different opinions about what the grammars allow. Below is my reason for
> believing that the grammars may allow for the unattached fragments.
> <msc expression> ::= <start> <node expression>*
> <start> ::= not significant
> <node expression> ::= <label name>:{<node> seq (<label name> {alt <label
> name>}*) | end } <end>
> <node> ::= (<msc ref expr>) | empty | <msc name> | <par expression> |
> condition <condition name list> | connect
> I cannot see anything here that connects the node expressions on top
> level of the <msc expression> other than the names of the labels. A node
> expression may very well start by a condition. Of course the total MSC
> must always contain one start symbol, but this is not the issue.
> In the graphical grammar, the situation is slightly more involved since
> the connection lines combine symbols.
> Firstly the top level production:
> <mscexpr area> ::=
> { <start area> <node expression area>* <hmsc end area>*
> } set
> makes no assumption about how the individual areas are connected. That
> is given in the productions using the meta-notation "is attached to".
> Therefore I concluded that there are any unconnected set of <node
> expression area>s, each of which may start with a <node area> which may
> be an <hmsc condition area>. There is no definite requirement anywhere
> that I could see that these <node expression area>s should be connected.
> I appreciate the reactions from more people with intimate knowledge of
> the MSC-96 grammars to make their opinions known.
> Yours
> Oystein Haugen

Dear Oystein, Jan, Dagbjorn and the others,

I have to agree with Oystein that the textual syntax does not
require every node to be reachable from the start node.
But, the static semantics of section 5.5 High-level MSC
clearly states:

   "Every node in the HMSC graph must be reachable from the
    <start>, i.e. the graph must be connected."

As a consequence indeed every node in an HMSC must be reachable
from the start node.

Best regards,
Michel Reniers

Michel Reniers, c/o Eindhoven University of Technology,
P.O. Box 513, NL-5600 MB Eindhoven, The Netherlands
Phone: +31-402475157          E-mail:
Fax  : +31-402463992

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