From:
higgins-dev-bounces@xxxxxxxxxxx [mailto:higgins-dev-bounces@xxxxxxxxxxx] On Behalf Of Anthony Nadalin
Sent: Thursday, September 11, 2008
7:33 PM
To: Higgins (Trust Framework)
Project developer discussions
Cc: 'Higgins (Trust Framework)
Project developer discussions'; higgins-dev-bounces@xxxxxxxxxxx
Subject: Re: EntityId decision
analysis page (was RE: [higgins-dev] entityIDnot an attribute?)
wiki is the pits
so a EntityID can't always be the unique identifier at best an EntityID is a
reference within a context only, Lets take a cell phone, it has a unique
identity of +015128380085 but that may not tell be how I reference this entity
within a context.
Anthony Nadalin | Work 512.838.0085 | Cell 512.289.4122
"Drummond
Reed" ---09/11/2008 08:24:04 PM---I took the action item on the Higgins
call today to parse the key questions being raised about EntityId on this
thread into a d
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From:
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"Drummond
Reed" <drummond.reed@xxxxxxxxxxxx>
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To:
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"'Higgins
(Trust Framework) Project developer discussions'"
<higgins-dev@xxxxxxxxxxx>
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Date:
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09/11/2008 08:24 PM
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Subject:
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EntityId decision
analysis page (was RE: [higgins-dev] entityID not an attribute?)
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I took the action item on the Higgins call today to parse the key
questions being raised about EntityId on this thread into a decision analysis
page on the Higgins wiki. I have posted this page at:
http://wiki.eclipse.org/EntityId_Requirements
…and
placed a link to it on http://wiki.eclipse.org/Context_Data_Model_1.1_Open_Issues#Open_Issues.
The
ideal way to proceed is for folks to post opinions to the page and then ping
the list with a pointer. However, for those who prefer responding in email,
following is the wikitext version of the page to which you can respond
directly.
=Drummond
== About
==
This
page is for discussing/documenting the terminology, requirements, and design
decisions for [[EntityId]]s.
==
Content Data Model Requirements ==
In terms
of the underlying graph model, following is a summary of the abstract
requirements derived in a recent (2008-09-11) thread on the email list. The
first step is determining if there is consensus about these requirements.
'''Please post a note with your wiki signature if you disagree with any of the
following:'''
# An
[[Entity]] is a node in the graph described by the Higgins [[Context Data
Model]]. The CDM needs a consistent way of representing arcs referencing that
node.
# There
MAY be 0..n such arcs referencing the node. (0 is possible for blank nodes.)
# An arc
MAY theoretically be represented as either:
## A
unique identifier.
## A set
of [[Attribute]]s of that [[Entity]], none of which itself is required to be a
unique identifier.
# If the
arc is represented as a unique identifier:
## It
MUST be locally unique within the [[Context]], and it MAY be globally unique
across all [[Context]]s).
==
Higgins API Requirements ==
The
second step, based on the above requirements, is answering the following
questions with respect to the Higgins API. '''Please post your votes/answers
(with your wiki signature).'''
=== #1:
Unique Identifier vs. Attribute Set ===
Should
the Higgins API constrain an [[EntityId]] to be a unique identifier, or can it
be a set of [[Attribute]]s?
=== #2:
Representation of an EntityId as a Unique Identifier ===
If an
[[EntityId]] is a unique identifier, should this be represented as:
# A type
of [[Attribute]]?
# A
separate property of an [[Entity]] that MAY be exposed as an [[Attribute]]?
#
Inherent in the definition of an [[Entity]]?
=== #3:
Cardinality ===
What is
the cardinality of [[EntityId]]? (The answer may depend on the answer to #2.)
# 0..n?
# 0..1?
# 1
(whose value may be null)?
From: higgins-dev-bounces@xxxxxxxxxxx [mailto:higgins-dev-bounces@xxxxxxxxxxx]
On Behalf Of Anthony Nadalin
Sent: Thursday, September 11, 2008 7:36 AM
To: Higgins (Trust Framework) Project developer discussions
Cc: higgins-dev; higgins-dev-bounces@xxxxxxxxxxx
Subject: Re: [higgins-dev] entityID not an attribute?
So there
are a couple of things here, we have always talked about the EntityID as being
a reference to the Entity and not the unique identifier. There are many ways to
reference an Entity, so I don't believe that this is limited to 0..1. I also
believe that the EntityID encapsulates a given set of attributes.The unique
identifier is only has to be unique within a context. So I believe that the
unique identifier is an attribute, not a way to reference the Entity.
Anthony Nadalin | Work 512.838.0085 | Cell 512.289.4122
Paul
Trevithick ---09/10/2008 05:51:39 PM---Raj has suggested the need to clarify
the language here. So here is a restatement. Additions in red. Substitutions in
blue. All
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From:
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Paul Trevithick <paul@xxxxxxxxxxxxxxxxx>
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To:
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higgins-dev <higgins-dev@xxxxxxxxxxx>
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Date:
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09/10/2008 05:51 PM
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Subject:
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Re: [higgins-dev] entityID not an attribute?
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Raj has suggested the need to clarify the language here. So here is a
restatement. Additions in red.
Substitutions in blue.
All defined terms in initial caps.
Background: We remain committed to these two principles:
- An Entity has 0..1 unique identifier (called an EntityId) (...and we expect
almost all Entities will have an EntityId).
- [Raj: you
asked about why this EntityId is optional. The answers are (1) that
our “complex” Attributes have values that are
themselves Entities and we didn’t want to require developers
to explicitly “name” these values (especially in
situations where there was no need for N>1 Entities to share
(link to the same) value/Entity and (2) we need this in order that
our model remain a pure super-set of RDF/OWL (and thus allows IdAS
to losslessly “adapt” the Semantic Web (including all
Linked Data).]
- An Entity has 0..N
Attributes some of which may be used singly or in combination to identify an Entity
or a set of Entities within a Context.
- [Raj: To
date we have decided not to define an explicit
“Identifier” Attribute type. The reason for not
defining it is twofold: First,
the distinction between an Identifier and an Attribute has so far
proved impossible to agree on. Second,
Context Provider developers are free to create their own Attribute
Definitions and thus a developer could define their own
“Identifier” sub-Attribute]
The proposal remains:
- To no longer
consider the one, optional EntityId as an Attribute.
- To have an IdAS
getEntityId() method to return this EntityId (or return null if it
doesn’t exist) whereas other getAttribute methods return
Attributes/values
- NOTE: CP developers
remain free to present the EntityId value as the value of some
Attribute type that they define and use within their Context
With the above clarified and annotated definitions, I’m interested to
hear Tony’s, Raj’s and anyone else’s reactions.
-Paul
On 9/9/08 1:20 PM, "Nataraj Nagaratnam" <natarajn@xxxxxxxxxx>
wrote:
Yea, there seems to be
disconnect here with usage of the term 'identifier' (or Id).
The statement "An
Entity has 0..N Attributes some of which may be used as identifiers" tells
me that there is more than one identifier, and then the statement "An
Entity has 0..1 EntityId" says that there is one identifier (as i think
"EntityId" means "Entity Identifier"). This seems to be
contradicting statements in some sense, and maybe the cause of disconnect here.
So how about this..
· An Entity has 0..N
Attributes
· An
Entity has 1 UniqueIdentifier within a given context.
Then it makes the calculation of uniqueIdentifier to be relevant to the Entity
within a given context; this way, we leave attributes as they are - if we end
up using those attributes to identify/search/lookup an entity, then fine but
uniqueness is not guaranteed. Wrt those attributes that are used to
search/lookup,.. maybe we don't need to designate those attributes to be
identifiers in a formal manner in the data model?
So proposal can be
To have an IdAS getUniqueEntityId() method to return a unique identifier within
the context of that entity, whereas other getAttribute methods return
Attributes/values
another comment - do we really want entities without unique identifiers at all?
Regards,
Raj
Anthony Nadalin---09/09/2008 12:40:37 PM---OK, So not sure I
agree
From:
Anthony Nadalin/Austin/IBM@IBMUS
To:
"Higgins \(Trust Framework\) Project developer discussions" <higgins-dev@xxxxxxxxxxx>
Cc:
higgins-dev <higgins-dev@xxxxxxxxxxx>,
higgins-dev-bounces@xxxxxxxxxxx
Date:
09/09/2008 12:40 PM
Subject:
Re: [higgins-dev] entityID not an attribute?
OK, So not sure I agree
I believe that there are 0..N EntityIDs and the EnitityID job is to encapsulate
the referenced attributes, thus there may be multiple EntityIDs.
Anthony Nadalin | Work 512.838.0085 | Cell 512.289.4122
Paul Trevithick ---09/09/2008 10:56:26 AM---Just to make sure
we’re all discussing the right proposal. Let me back up a bit here and
restate it:
From:
Paul Trevithick <paul@xxxxxxxxxxxxxxxxx>
To:
higgins-dev <higgins-dev@xxxxxxxxxxx>
Date:
09/09/2008 10:56 AM
Subject:
Re: [higgins-dev] entityID not an attribute?
Just to make sure we’re all discussing the right proposal. Let me back up
a bit here and restate it:
Background: We remain committed to these two principles:
· An Entity has 0..1 EntityId
(...and we expect almost all Entities will have an EntityId)
· An
Entity has 0..N Attributes some of which may be used as identifiers (that is,
these attributes may singly or in combination uniquely identify an Entity
within its Context)
The proposal is:
· To no longer consider the
one, optional EntityId as an Attribute.
· To
have an IdAS getEntityId() method to return this EntityId (or return null if it
doesn’t exist) whereas other getAttribute methods return Attributes/values
· NOTE:
CP developers remain free to present the EntityId value as the value of some
Attribute type that they define and use within their Context
-Paul
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