Fwd: [xml-dev] Here's how to remove 'time' from a processing problem

[Dimitre Novatchev <dnovatchev@gmail.com>]

---------- Forwarded message ---------
From: Dimitre Novatchev <dnovatchev@gmail.com>
Date: Wed, Dec 21, 2022 at 8:30 AM
Subject: Re: [xml-dev] Here's how to remove 'time' from a processing problem
To: Roger L Costello <costello@mitre.org>

Just run the simple transformation periodically with a Runner, that is not an XSLT program. Like using Windows Task Scheduler.

From a software engineering standpoint this is probably an optimal design:

   -   There is almost no (0) coupling between the Transformer application and the Runner. The Transformer just does a simple thing once and doesn't even know that it is invoked periodically by a Runner - doesn't know anything about anything called a "Runner".

   -  The Runner doesn't know anything specific about what the Transformer is and what it is actually doing. For the Runner the Transformer is just one of many regular tasks (maybe defined in a database table) to invoke regularly within a specified period and with specified parameters.

This achieves simplicity, loose coupling and low complexity. As the parts are small and simple, there is a lesser probability that something could go wrong within each of the parts, thus we also achieve greater reliability.

A more complex design would be to implement an IObservable (the thing that confirms the threat)   and an IObserver that is subscribed for the occurrence of a particular event (an occurrence of a threat). See https://en.wikipedia.org/wiki/Observer_pattern

AFAIK the XPath and XSLT languages at present do not allow for an easy and elegant way of implementing this design pattern.

Thanks,

Dimitre

On Wed, Dec 21, 2022 at 8:02 AM Roger L Costello <costello@mitre.org> wrote:

Hi Peter,

You don't like my fictitious Car.xml/PoliceReport.xml example? Bummer.

Okay, then here's an actual, real-world example. It is an exact analog of the Car.xml/Police.xml example, albeit a bit more complex.

A radar scans the sky and detects an object. The radar saves the information about the object to an XML file and stores the file in a folder (along with other files that it has stored for other objects):

<Object id="XYZ">
    <Location>
        <Latitude>10</Latitude>
        <Longitude>20</Longitude>
        <Elevation>100</Elevation>
    </Location>
    <DateTime>...</DateTime>
    -- other info --
</Object>

At some point a program reads in that XML document and begins processing it. The objective of processing is to output an alert if the object represents an enemy aircraft and "" (benign object) otherwise. However, the program determines that the document does not contain sufficient information to make a decision. The information to make the decision arrives some time later, in another document (the radar has subsequently collected additional information about the object):

<UpdatedInfo>
    <Object id="XYZ">
        <FlightProfile>......<FlightProfile>
    </Object>
</PoliceReport>

So the desired processing behavior is this:

Read the next XML document.
If the XML document contains data about an object and there is insufficient information to process it then
    Wait until more info about the object arrives ....
    .......... time elapses ........... the updated
    info arrives: analyze the new info and
    if it indicates the object is an enemy aircraft then
    output an alert message else output ""

That algorithm involves dealing with time.

Here's how to eliminate time from the equation.

-- As I described earlier --

/Roger

--

Cheers,

Dimitre Novatchev

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