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Hi,
Reg the ripple effects of updates of XML documents that you have
mentioned would some kind of "normal forms" like in relational design be
of help when designing the schemas for the XML documents. However, I do
not know if such kind of normal forms exist for guiding XML schema designs.
Regards,
Kiran.
dbexcom wrote:
> I am concerned to hear this approach, and others here, discussed,
> without comment as to scaling issues regarding very large datastores
> (in XML documents or in relational dbms) that might be ten to several
> hundred terabytes in size.
>
> Specifically, in the following respects:
> 1- sheer size problems such as disk access time, out of memory
> conditions, and processor time to parse very large XML documents (say,
> 1,000 documents of 1 terabyte each) or a very large number of XML
> documents of smaller size (say, 5,000,000 5MB docs).
> 2- maintenance issues driven by the smallest of interface changes or
> presentation changes, that result in hundred of thousands if not
> millions of manual static schema modifications, rippling across either
> a very large number of smaller XML documents and their specific
> schemas or through as many as a thousand or so documents of 1 terabyte
> each in size. Even if such ripple effect maintenance can be automated,
> the processing time required to update, say, 5,000,000 XML doc files
> of 5MB each cannot be said to be real time, so perhaps weeks of
> processing time is required before the interface mods can be subject
> to just one full test.
> 3- consistency across versions, releases, XML standards and tool sets
> (MS, SQL Server, MySQL, Oracle, etc) considering that a very large
> scale project will take some time to mature (possibly years), and that
> a lack of backward compatibility could drive massive changes into the
> basic XML design structure and overall document architecture.
> 4- transmission time across interchanges - whether lan, web or
> intranet based, the time to transmit and parse result sets to XQuery
> are often very large, and for very large XML documents this processing
> time is unacceptably long. People want results in five to eleven
> seconds, not minutes, not hours.
>
> I have specific experience in very large paper based, and relational
> database systems. From time to time, I see folks scale up systems that
> work fine, up to a point, past which they are forced to redesign from
> scratch.
>
> While I agree that broadly generalized discussions are the most common
> form of technical exchange of information, having seen several of
> these pilot efforts crash and burn, I feel a moral obligation to
> suggest that some comment be made as to scaling issues, known
> propagation or ripple effects, and sheer size problems that come into
> play when viable "average" architectures are scaled beyond their
> design parameters.
>
> In reference to this specific method, I submit that when dealing with
> a very large repository of prose, that a very large number of "profile
> documents" is possible, and that the number of possible "profile
> documents" correlates to some index of the context and the subject
> matter and the usage purposes (inquiry / result pairs), a result that
> to my mind increases or scales up as the number of prose entities
> scales up. I will go further and say that, for instance, for all
> articles ever published in the scientific journal "Nature", or perhaps
> all items in the U.S. Library of Congress or all pending applications
> and issued patent files in the U.S. Patent Office, this number of
> possible "profile documents" becomes very large indeed. Though it may
> be possible to satisfy as much as a majority if inquiries with a small
> number of such structures, the rest of the inquiries, it seems to me,
> will require an ever increasing number of "profile documents" to
> satisfy so that satisfying the last 1 percent of such inquiries might
> require several thousands of such "profile documents", if not tens of
> thousands or hundreds of thousands.
>
> So, I am interested to hear about practical applications using XML
> only implementation (XQuery, XML, XSLT, XPath, etc) that deal with
> wide ranging subject matter, such as is found in the scientific
> journal "Nature", or perhaps all items in the U.S. Library of Congress
> or all pending applications and issued patent files in the U.S. Patent
> Office, to a very broad audience, across scientific disciplines and
> cultures (and possibly languages), for a very large data repository of
> mixed content (prose, graphics, slides, photos, video, sound, other
> streaming data sources or media) measured in tens or hundreds of
> terabytes.
>
> While XML is superb at document mark up, in my experience almost as
> good as TeX, it does not strike me as the best tool for the job when
> dealing with very large scale data repositories. Still, I have an open
> mind and perhaps someone here can enlighten me.
>
> Thank you.
>
>
>
> At 10:28 PM 8/18/2003 -0400, you wrote:
>
>> One of the difficulties in considering factoring out functionally
>> dependent entities from prose, is that the block of prose may itself
>> not be worth reusing. That is, the prose may be a one-shot document
>> whose original intent is simply to present information, not to act as
>> a reliable container for access by clients with a variety of intents.
>> One thing I've done is to try to identify those concepts which are
>> best understood, are most firmly established, and which serve as the
>> focus of the stakeholders' activities and communications. Then
>> design a profile document for each of these high-level concepts,
>> which provide context for making pointers and for generating
>> identifiers. The profiles are designed to provide some elements which
>> are rigidly structured, and other elements which are prose with mixed
>> content. In one case at least, this allowed me (with a stylesheet) to
>> resolve most cross references internal to the document itself,
>> minimizing calls to scan external documents. Also, depending upon the
>> nature of your data and your validation techniques, you may be able
>> to use the mixed content prose as the source of the definitive
>> information, rather than just as glue.
>> It is certainly something a good CMS can help with, but I've also
>> used DSSSL and XSLT/XPath for doing just this sort of thing with
>> reasonable results. You might also want to check out DITA by Michael
>> Priestley et al. of IBM, which I think intends to facilitate topical
>> reuse.
>>
>> Roger L. Costello wrote:
>>
>>> Hi Folks,
>>> I am working with some people who wish to migrate from an
>>> all-prose format to a prose-plus-reusable-XML-fragments
>>> format.
>>> They have some data in prose that is useable in many contexts. They
>>> want to break out that reusable data into XML fragments. However,
>>> they want to continue to provide the prose style.
>>> For example, consider this prose data:
>>> <para>The city of Miami, Florida (pop. 1, 234,000) is a sprawling city
>>> with many attractions. Miami Beach is a popular attraction. The
>>> spring tide is ... The neap tide is ... </para>
>>> Examining this prose we can extract reusable info about the city of
>>> Miami:
>>> <City id="Miami">
>>> <state>Florida</state>
>>> <population>1,234,000</population>
>>> </City>
>>> We can also extract reusable info about tide data on Miami Beach:
>>> <TideData id="MiamiBeachTides">
>>> <springTide>...</springTide>
>>> <neapTide>...</neapTide>
>>> </TideData>
>>> The problem now is to create a framework which allows the prose
>>> to bring-together the independent, reusable XML components.
>>> Conceptually, what is desired is a "glue framework" like this:
>>> <para>The <ref href="Miami.xml"> is a sprawling city with
>>> many attractions. Miami Beach is a popular attraction. The
>>> tides are <ref href="MiamiBeachTides.xml"><para>
>>> Thus, the prose is "glueing" together the XML fragments.
>>> Is this a problem that you have experience with? What "glue
>>> framework" have you used? What strategy did you use to merge
>>> the XML fragments with the prose? Is there is a standard way
>>> of combining semi-structured data with structured data?
>>> /Roger
>>>
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>>
>>
>>
>>
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>
>
>
>
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