RE: [tosca] [OASIS Issue Tracker] Commented: (TOSCA-60) Primer - All MATERIAL Contributions

["Probst, Richard" <richard.probst@sap.com>]

I agree, tier is more tangible than layer, but we should not describe tier as physical. A tier may be implemented as a virtual resource. Two tiers could run as VMs on the same physical resource.

Best,
  --Richard


-----Original Message-----
From: tosca@lists.oasis-open.org [mailto:tosca@lists.oasis-open.org] On Behalf Of Frank Leymann
Sent: Thursday, December 06, 2012 2:10 AM
To: OASIS Issues Tracker; tosca@lists.oasis-open.org
Subject: Re: [tosca] [OASIS Issue Tracker] Commented: (TOSCA-60) Primer - All MATERIAL Contributions

I do agree with you, Tobias:  Layer is most often about software
abstraction, while tier most often refers to more "tangible" components.

Not sure whether we should change terminology because at the end there is
no "standardized definition"....

Gruss/Regards,
Frank





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Datum: Donnerstag, 6. Dezember 2012 07:12
An: "tosca@lists.oasis-open.org" <tosca@lists.oasis-open.org>
Betreff: [tosca] [OASIS Issue Tracker] Commented: (TOSCA-60) Primer - All
MATERIAL Contributions

>
>    [ 
>http://tools.oasis-open.org/issues/browse/TOSCA-60?page=com.atlassian.jira
>.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=31912#acti
>on_31912 ] 
>
>Tobias Kunze  commented on TOSCA-60:
>------------------------------------
>
>Re the tier vs layer question: I wonder whether there is any accepted
>definition. For instance, Sun's JEE Design Concepts[1] use "tier" for
>logical organization and "layer" for "layers of the stack". Then there is
>the OOD meaning of "units of dependency" (similar to "module"), which is
>close to the "stack" meaning, but not the same, and so forth.
>
>Looking at the sundry architecture books I have lying around:
>
>* Bass, Clements, Kazman: "Software Architecture in Practice", 2nd Ed.,
>Addison-Wesley, 2003
>  => Talks about "layers" a lot, both in the sense of "separated
>concerns" and "stack". They use "tier" in the sense of "distributed"
>* Dyson, Longshaw: "Architecting Enterprise Solutions: Patterns for
>High-Capability Internet-based Systems", Wiley, 2004
>  => "tier" = "network-connected"/"distributed", "layer" =
>"stack"/"module"
>* Gorton: "Essential Software Architecture", Springer, 2006
>  => Ditto.
>* Shi, Murthy: "Architectural Issues of Web-Enabled Electronic Business",
>Idea Group, 2003
>  => Ditto.
>* Shklar, Rosen: "Web Application Architecture: Principles, Protocols and
>Practices", Wiley, 2003
>  => Ditto.
>* Buschmann, Henney, Schmidt: "Pattern-Oriented Software Architecture IV:
>A Pattern Language for Distributed Computing", Wiley, 2007
>  => is odd, uses "tier" only once in the context of a 3-tier
>application, but the associated figure uses "layer" instead (Section 2.1)
>  => however, throughout the rest of the book, "layer" is consistent with
>the uses above ("module")
>* Buschmann, Henney, Schmidt: "Pattern-Oriented Software Architecture V:
>On Patterns and Pattern Languages", Wiley, 2007
>  => uses "tier" in the physical ("distributed") sense, whereas "layer"
>is logical as in "application concern", although it doesn't seem to be
>defined anywhere
>* Buschmann, Meunier, Rohnert, Sommerlad, Stal: "Pattern-Oriented
>Software Architecture I: A System of Patterns", Wiley, 1996
>  => Ditto.
>* Schmidt, Stal, Rohnert, Buschmann: "Pattern-Oriented Software
>Architecture II: Patterns for Concurrent and Networked Objects", Wiley,
>2000
>  => Ditto (unsurprisingly)
>* Kircher, Jain: "Pattern-Oriented Software Architecture III: Patterns
>for Resource Management", Wiley, 2004
>  => "tier" = "networked", "layer" = "stack" (calls out middleware as a
>"layer")
>* Schlossnagle: "Scalable Internet Architectures", Sams, 2006
>  => "tier" = "distributed", "layer" = "stack" (in the OSI sense, but
>it's really closer to application "concerns"/"modules")
>
>Bottom line AFAICS is that, while both are logical terms, "tier" is an
>abstraction of the IT components making up an application, whereas
>"layer" is an abstraction of the software code design. E.g. "database
>layer" refers to the code dealing with the database (e.g. an ORM), where
>as "database tier" is the actual database (e.g. MySQL).
>
>It is striking that none of the publications listed actually *define*
>these terms. Instead, they are simply used in a common-sense way.
>
>[1] 
>http://scea.djcheng.com/page.php/3/Application_Design_Concepts_and_Princip
>les.html
>
>
>> Primer - All MATERIAL Contributions
>> ------------------------------------
>>
>>                 Key: TOSCA-60
>>                 URL: http://tools.oasis-open.org/issues/browse/TOSCA-60
>>             Project: OASIS Topology and Orchestration Specification for
>>Cloud Applications (TOSCA) TC
>>          Issue Type: Task
>>          Components: Primer
>>            Reporter: Paul Lipton
>>            Assignee: Dale Moberg
>>
>> This issue is a bucket for ALL MATERIAL contributions such as
>>explanatory paragraphs, examples, etc.
>> IMPORTANT:  ALL contributions will be aggregated by the Primer editors
>>and considered for approval by the TC, although they may work with
>>contributors to align style, format, etc. No contribution will be
>>discarded without the approval of the contributor.
>> * See this email for details on the Primer development process, etc.:
>>https://www.oasis-open.org/apps/org/workgroup/tosca/email/archives/201211
>>/msg00003.html) 
>> See TOSCA-16 for ALL NON-MATERIAL suggestions such as spelling and
>>grammar changes. 
>
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