| RE: EntityId decision analysis page (was RE:[higgins-dev]entityIDnot an attribute?) |
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On #2 I vote no -- it's not required to be an attribute however there's no requirement that restricts its value from also being reflected in an attribute. On #3, I vote 0..1 (where entities which are missing an entityID can only be used as "blank entities". The other use case is where one performs a search and receives one or more Entities that are nameless. Do people want/need that to happen? On #1... I dunno. I tend to want simple. Another question is this: Is the EntityID of an Entity immutable? I believe it must be as soon as we start tying policy to EntityIDs. Either that, or we need to require a way to ensure referential integrity for places where EntityIDs are stored in policy statements.
Jim
+1 that “Contextually Unique Identifier” (CUID) accurately captures the requirements for the value of the Context Data Model component currently called “EntityID”.
So Jim, are you suggesting that we change “EntityId” to “CUID”? Or just that we just the term CUID when stating the requirements for an EntityId value?
Also, please feel free to weigh in on three other questions I posed yesterday:
1) Must an EntityId be an identifier (string) or can it be a collection of attributes (multi-part key)? (Higgins 1.0, only supports the former.)
2) Must an EntityId be exposed as an attribute of an Entity, or is it optional to do that?
3) Is the cardinality of EntityId 0..n or 0..1?
=Drummond
From: higgins-dev-bounces@xxxxxxxxxxx [mailto:higgins-dev-bounces@xxxxxxxxxxx] On Behalf Of
Jim Sermersheim Sent:
Friday, September 12, 2008 1:03 AM To:
higgins-dev-bounces@xxxxxxxxxxx Cc:
'Higgins (Trust Framework) Project developer discussions' Subject: Re: EntityId decision analysis page (was RE: [higgins-dev]entityIDnot an attribute?)
Right, we talked about this on the dev call today. EntityID should not be called "unique identifier" because that might imply "globally unique". What ppl have actually meant in the convo by "unique identifier" is "an identifier -- unique within the context -- that names the entity within that context".
Our original term (CUID) was much better [Contextually Unique Identifier]
wiki is the pits "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
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:
…and placed a link to it on .
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
Thursday, September 11, 2008 7:36 AM
Higgins (Trust Framework) Project developer discussions
higgins-dev; higgins-dev-bounces@xxxxxxxxxxx
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
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 :
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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
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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
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
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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:
Cc:
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:
To:
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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