A response:
On 1/11/11 2:08 AM, Peter Niblett wrote:
2. The other
part of the issue concerns
the name of the event body filter. As I said in my email of Sept
22, there are three things that the filter syntax has to express.
i) The type of data that the filter operates against (the
subject)
ii). The language used to
express the
filter (the dialect)
iii). The filter expression
itself.
It is helpful to retain the
separation
of i) and ii), as it allows you to tell what the subject is,
even
if you don't recognise the dialect. If we just had a flat name
I could
define my own filter expression - say Peter_special_no_22 -
and it
would not be possible to tell what kind of filter it is. Also
if
you do a have a dialect used for more than one subject (e.g.
XPath used
for both body and metadata) you only have to define its syntax
and semantics
once. I actually
prefer a syntax where the dialect is expressed as an attribute
(that's
what happens in WS-Notification and WS-Eventing), e.g.
<body dialect="xpath1">
A/B </body>
but I understand that the TC
prefers
an approach where we include the dialect as part of the
element name, so
I am ok with that,
I actually would be OK with that approach as well. So I wouldn't
assume the will of the TC on this point. I have done so, because I
was not attending Assembly TC meetings when this element was first
introduced, and nobody has stepped up to offer this alternative.
But perhaps that was a mistake?
3. This is what we have in the
current
working draft
<filters>
<eventType.sca
qnames="list of xs:QName"? namespaces="list of xs:anyURI"?
/>*
<body.xpath1>
xs:string
</body.xpath1>*
<any>*
</filters> ?
I agree with Anish that we
don't need
the word "filter" in the filter QName, since these elements
are
all children of the <filters> element.
As I stated in my proposal, I actually think the other entry should
be changed to "eventTypeFilter.sca". I think this is an odd place to
start applying brevity to something represented in XML. If we're
talking about global element definitions, then I think a fully
spelled out name is appropriate. If we want to change the schema so
that these elements are defined locally to the "filters" element,
then I'd agree that we can drop the "filter" from the name.
4. I think it we should have
a
consistent appearance for the two filter names (and any others
we may introduce
in the future). Changing <body.xpath1> to
<xpath1Body>
or <bodyXpath1> makes the body filter syntax and the
eventTye filter
syntax inconsistent (in comparison with the consistent syntax
we currently
have).
As I understand things, the
issue now
is that we cannot use a . in the body name, since the element
isn't defined
using a substitution group and everywhere else in SCA assembly
a . implies
the substitution group. This is indeed the case.. here is the
current schema
definition:
<element name="filters"
type="sca:Filter"/>
<complexType
name="Filter">
<sequence>
<choice minOccurs="0" maxOccurs="unbounded">
<element ref="sca:eventType" />
<element ref="sca:body.xpath1"
/>
</choice>
<any namespace="##other" processContents="lax"
minOccurs="0"
maxOccurs="unbounded"/>
</sequence>
<anyAttribute
namespace="##other" processContents="lax"/>
</complexType>
<element
name="eventType"
abstract="true"/>
<element
name="eventType.sca"
type=sca:EventType.sca"
substitutionGroup="eventType"/>
<complexType
name="EventType.sca">
<sequence>
<any namespace="##other" processContents="lax"
minOccurs="0"
maxOccurs="unbounded"/>
</sequence>
<attribute
name="qnames" type="sca:listOfQNames" />
<attribute
name="namespaces" type="sca:listOfAnyURIs" />
<anyAttribute
namespace="##other" processContents="lax" />
</complexType>
<element
name="body.xpath1"
type="string" />
As you can see that
<eventType>
is an abstract element with only one substitution group member
defined
(eventType.sca) but <body> is defined as a concrete
element.
Hmmm. I'd actually argue the other way around. The use of
substitution group here is spurious. It is, quite simply the SCA
defined eventType filter of event types. It's overspecified to
allow eventType to be extended, because we don't *do* anything with
that capability.
If you don't like the standard filter the spec defines, just take
advantage of the "<any namespace="##other" ..." declaration.
I propose we keep the . in body filter - if we need any
changes at
all they are
i) Update the schema so that
we
have an abstract element for the body filter, just like we do
for the eventType
filter. That would regularise the appearance of the .
character in the
name
Why?
ii) Capitalise the X and the
P, i.e.
<body.XPath1> since it is usually referred to as XPath,
not xpath
or xPath or Xpath.
I hate to spend so much time on naming, but to summarize:
a) Since it is defined as a global element "body.xpath1" should
include the word filter in its name. We either do that, or we turn
it into a local element. Same with "eventType.sca".
b) Using substitution groups here is spurious. In the other places
we've done that, there's been actual specification text about what
those extensions are. Here, we have no such purpose, so we
shouldn't do it. So "." shouldn't appear in the name, and we should
probably eliminate the substitution group for eventType.sca, and
just call it "eventTypeFilter".
c) I'm OK with moving the "XPath1" portion of the meaning to an
attribute, which could simplify this question by letting us call it
"bodyFilter", which has the benefit of being intuitive.
-Eric.
Regards
Peter Niblett
IBM Senior Technical Staff Member
Member of the IBM Academy of Technology
+44 1962 815055
+44 7825 657662 (mobile)
From:
Anish Karmarkar
<>
To:
Date:
21/12/2010 07:50
Subject:
Re: [sca-assembly]
Action item 2010-12-07-3, ASSEMBLY-239
Thanks for the detailed explanation for your
choice. Two
comments inlined below.
-Anish
--
On 12/20/2010 4:12 PM, Eric Johnson wrote:
In the call from two weeks back, I think we had
agreement
about 1/2 of the proposed resolution to ASSEMBLY-239.
We had an issue, however, with the proposed name change -
changing
"body.xpath1" to "eventBodyFilter".
My action item - to come up with alternate name proposals.
Question: what to use as a separator? Choices: period
("."),
underscore ("_"), or camelCase? Why care?
Period used elsewhere to indicate a pattern of a base
substitution group.
Here such a substitution group is unnecessary, as the element
already
appears in a situation of explicit extensibility, where any
element is
allowed, rather than elements that extend a specific construct.
Further,
the situation does not require any base set of information that
must be
provided by the elements.
Underscore is not used elsewhere. Introducing it here might be
confusing
or at least distracting.
Conclusion: use camelCase pattern, which is used elsewhere.
Seems like a reasonable choice to me.
Question: What words do we need to include
in the
name of the element? Options: "body", "xpath1"
(or variations), "event", "filter"
For example:
body xpath1
xpath1 filter
body xpath1 filter
body filter xpath1
filter body xpath1 (or, even more self-explanatory: "filter body
with
xpath1"
event body filter xpath1
As per discussions, I understand a strong desire from some
members of the
TC that "xpath1" appear in the name of the element, to
distinguish
it from other possible languages for body filters.
Putting both "event" and "filter" in, for the moment
is mostly redundant, because "filter" only refers to events.
If we only choose one, then should it be "event" or "filter"?
Since "event" occurs in more places in the spec than "filter",
I conclude that "filter" in the name connotes a more precise
meaning than "event".
Based on the above, comment on "event" vs. "filter",
this suggests that we should change "eventType" to "typeFilter",
as it carries more meaning (admittedly, at the cost of an
additional character).
Following the pattern of "typeFilter", then, it makes sense to
use some variation of "bodyFilter".
However, should it be "bodyFIlterXPath1", or "xpath1BodyFilter"?
Inventing some variations of "typeFilter", I came up with
"dynamicTypeFilter", "computedTypeFilter", and
"randomTypeFilter".
The most natural place for the qualifier seems to be at the
front, so I
conclude:
"xpath1BodyFilter"
This element (and all filter expressions) can occur
only
as a child of the <filter> element. So both 'filter' and
'event'
are a little redundant. I have a very mild preference for
'bodyXpath1',
but other combinations (including Eric's recommendation) are
fine too.
as my recommendation for the name of the element.
-Eric.
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