EntityId decision analysis page (was RE: [higgins-dev] entityID not an a

["Drummond Reed" <drummond.reed@xxxxxxxxxxxx>]

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

From:	Paul Trevithick <paul@xxxxxxxxxxxxxxxxx>
To:	higgins-dev <higgins-dev@xxxxxxxxxxx>
Date:	09/10/2008 05:51 PM
Subject:	Re: [higgins-dev] entityID not an attribute?

---

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