[Fwd: RE: [xml-dev] Enhancing the richness of an information system [was: Difference between an extensible versus an evolvable information system?]]

["Chiusano Joseph" <chiusano_joseph@bah.com>]

[Removing "OT", as this seems to be on-topic to me]

Ah...all characteristics of service-oriented architectures.

Kind Regards,
Joe Chiusano
Booz | Allen | Hamilton
Strategy and Technology Consultants to the World

-------- Original Message --------
Subject: RE: [xml-dev] [OT] Enhancing the richness of an information
         system [was: Difference between an extensible versus an
         evolvable information system?]
   Date: Wed, 2 Jun 2004 12:27:47 -0400
   From: "Alessandro Triglia" <sandro@mclink.it>
     To: "'Roger L. Costello'" <costello@mitre.org>,
         <xml-dev@lists.xml.org>

 Could we say that a system is extensible if one or more of its external
interfaces support the addition of new components - which thus become an
integral part of the resulting "extended" system?Also, could we say that
a system is extensible if one or more of its *internal* interfaces
support the addition of new components or the replacement of a component
with a new component with an extended interface?In both cases,
additional entire external interfaces can be made available as the
result of the extension.I still think that "evolvability" has totally
different connotations, which relate to the ease, cost, and elegance of
changes to be made to meet new requirements/constraints.  (Whereas
"extensibility" would only mean that an addition or replacement is
possible - i.e., explicitly supported by some interface - and can be
safely ignored by the user.)(Which means that one can have evolution
with or without extension - in many cases, breaking extensibility.)(Or
vice versa.  Say, adding a second keyboard to my PC may or may not be
considered as "evolution" of my PC.)Alessandro Triglia

     -----Original Message-----
     From: Roger L. Costello [mailto:costello@mitre.org]
     Sent: Wednesday, June 02, 2004 11:32
     To: xml-dev@lists.xml.org
     Subject: [xml-dev] [OT] Enhancing the richness of an
     information system [was: Difference between an extensible
     versus an evolvable information system?]

     Hi Folks,Many thanks to those who responded to my last
     message.  This message is a follow-up. From the
     responses it is evident that the difference between
     "extensibility" and "evolution" can be slippery.  I like the
     distinction that Ken Laskey gave:"To be extensible allows you
     to do things for which you have a current understanding but to
     do it over a wider range of instances."  (Thus, adding new
     keywords, or adding new book categories are examples of
     extending the system, not evolving the system)
     "To show evolution, you need to do something in a new way or
     do something you hadn't done before." In the following
     discussion I will use the terms "extensibility" and
     "evolution" using these definitions.I would like to hear your
     thoughts on ways to enhance the richness of an information
     system.I see two ways of enhancing the richness of an
     information system:1. Horizontal Extension2. Vertical
     EvolutionBelow I explain what I mean by these terms.Horizontal
     ExtensionA typical method of growing a system is to "add more
     stuff".  For example, Amazon can grow by adding more ways for
     users to locate information:     - add a keyword search
     capability,     - add a way to locate information based
     upon book category,     - add a way to locate information
     based upon author name,     - etc. By "adding more stuff"
     Amazon has extended its "access mechanisms".  The system has
     expanded horizontally with new access methods.  I refer to
     this method of enhancing the richness of a system as
     horizontal extension.Advantages: this method of enhancing the
     richness of an information system is well understood and is
     controllable.Disadvantages: no matter how many ways Amazon
     provides for accessing information, it will never be
     enough. The need for new ways to access information changes as
     information changes (e.g., new fields of study) and as users
     change.  (I offer as evidence the constantly changing face of
     the Amazon web site)Vertical EvolutionWhen I was a child I
     used to enjoy building things with Legos.  Starting from
     simple Lego building blocks I was able to build up rich
     structures.  The Lego building block "interface" was fixed
     (i.e., the blocks snapped together in certain ways).  But that
     simple interface was sufficient to enable creation of
     tremendously rich structures.  The richness of the structures
     was limited only by my imagination.Analogously, a method for
     enhancing the richness of a system is to "build up" the system
     from building blocks.  The system is thus designed to support
     different mechanisms for "connecting" the pieces.  After
     launching the system, the ways that the system changes is
     dictated by how the users connect the pieces together. For
     example, suppose that Amazon provides a "related to" mechanism
     for connecting information.  Further, suppose that Amazon does
     not have a keyword search capability.  The system could
     "evolve" to support keyword searches by using the "related to"
     mechanism:XSLT --------------------> XSLT: Programmer's
     Reference by Michael Kay             "related-to""XSLT" is a
     user-defined keyword."XSLT: Programmer's Reference by Michael
     Kay" is a basic information building block within the Amazon
     system.It is important to note that no new functionality was
     introduced.  Existing functionality was utilized to enhance
     the richness of the system.  That is, the "related to"
     connection mechanism was used to create the keyword search
     mechanism.  I refer to this method of enhancing the richness
     of a system as vertical evolution.Advantages: the system is
     able to quickly respond/adapt to user needs.  In fact, it is
     the users that evolve the system!  The system simply provides
     the mechanisms for the user to "snap together the building
     blocks". Disadvantages: it is important that the system
     provide guides to ensure that evolution occurs in a useful
     direction.  (The system guides, but does not control the
     evolution)What are your thoughts on this?  /Roger