Re: [ESDS] Interaction models for Discovery Services

[Mark Harrison <[e-mail]>]

Dear Ken, ESDS folks,

Ken - thanks for the clarifications regarding identifiers.

Yes, I had intended to say 'a URI or specifically an EPC URI string'  
since URI includes both URNs and URLs.
In practice, all currently defined EPC identifier schemes have URI  
representations (in fact URNs) - although it is conceivable that a URL  
could be used as the identifier (although a URN, Digital Object  
Identifier (DOI) or Handle might be less 'fragile' or more likely to  
be maintained for long-term resolution).

URIs and structured identifiers have the benefit of making it easy to  
express patterns or ranges of related identifiers (e.g. for objects of  
the same product type or issued by the same organization), since  
related URIs often share a common prefix or stem.  The EPCglobal Tag  
Data Standard defines URI patterns for EPC identifiers in which  
wildcard characters  (*) or [lo-hi] ranges indicate which absolute  
URIs should match the specified pattern.

[ Not sure whether this is based on an established convention for URI  
patterns (Ken would know this) - but either the same approach could be  
adopted for non-EPC URI patterns - or regular expressions could be  
used (although it might be trickier to express a multi-digit numeric  
range using a regular expression - see for example http://www.regular-expressions.info/numericranges.html 
  )]

The XSD schema files for the Application Level Events (ALE) and EPC  
Information Services (EPCIS) standards developed by the EPCglobal  
community do not in fact constrain an EPC to be anything other than a  
URI - so it seems quite likely that a future EPCglobal standard for  
Discovery Services would take a similar approach of 'any URI' for EPCs  
or individual IDs.

Using structured identifiers and in particular URIs and URI patterns  
could have advantages in the operations of a Discovery Service, since  
URI patterns could be used as a convenient shorthand for registering  
or querying about multiple IDs that have a common URI prefix and a  
contiguous range of serial numbers.  They could also be helpful for  
any high-level indices that might be used for expressing the scope or  
identifier types / ranges handled by a particular DS.

Regarding ensuring global uniqueness, as Ken pointed out in his  
earlier e-mail, it is possible to prepend a non-URI string with a URI  
prefix in order to qualify its namespace and thereby construct a  
globally unique URI identifier from a combination of one or more  
locally unique identifier strings.

Best regards,

- Mark



On 10 Jul 2008, at 13:41, Kenneth R. Traub wrote:

>> ESDS is considering not only Electronic Product Codes (EPC) but more
> general kinds of identifiers - so any references to 'EPC' or 'EPC
> identifier' could also be interpreted as an individual ID of an  
> object,
> whether expressed as a string, a URN or specifically an EPC URN  
> string.
>
> A small point, but I believe you mean to say "...a URI or  
> specifically an
> EPC URI string."  There's no reason to restrict identifiers to just  
> URNs
> (which are a subset of URIs).
>
> On the other hand, I'm not sure you'd want to allow non-URI strings,  
> as
> you'd have little hope of insuring their global uniqueness.
>
> The correct formulation is probably "absolute URI".
>
> Ken
>
> ---
> Ken Traub Consulting LLC
> [phone]
> [e-mail]
>
>

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