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136 lines
9.6 KiB
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<title>Handbook Troggle Architecture Speculations</title>
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<link rel="stylesheet" type="text/css" href="../../css/main2.css" />
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<body><style>body { background: #fff url(/images/style/bg-system.png) repeat-x 0 0 }</style>
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<h2 id="tophead">CUCC Expedition Handbook</h2>
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<h1>Troggle Architecture Speculations</h1>
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<pre>
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From: Philip Sargent (Gmail) [mailto:philip.sargent@gmail.com]
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Sent: 19 April 2020 01:28 [original - since edited with extra refs.]
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To: expo-tech@lists.wookware.org
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Subject: vague thoughts about future troggle architecture
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</pre>
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<p>
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At our last virtual pub Sam confirmed that using today's tools to
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re-partition troggle with all the user interface in the user's browser would
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be utterly horrible using current tools (javascript frameworks: react,
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angular etc.).
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<p>
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These front-end frameworks get out of date in couple of years or so. So they don't
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give us the decade-long stability we need to match available maintenance
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effort. [ See <a href="https://en.wikipedia.org/wiki/Comparison_of_JavaScript_frameworks">
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Wikipedia list of javascript frameworks</a>.] With our deep historical perspective ("cough"),
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we can expect this menagerie to sort itself out into a stable, standardised foundation
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within the next 10 years.
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<p>
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A web API to expose the troggle database (read-only) would allow some keen
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person to write a special-purpose app on a phone, e.g. an entrance-locator
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app, talking directly to the database. But replacing the whole user
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interface does not seem feasible yet. In 10 years: probably.
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<p>
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It did occur to me that we are missing a trick: 99+% of the database doesn't
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change except for survey data updates which, apart from during expo, happen
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only every week or so. And the database is only 10 MB so is entirely
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feasible to copy absolutely everything into the browser except for scanned
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images and photos.
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<p>
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So we could partition troggle so that all the user display bits run in the
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browser (or a progressive web app) using a python interpreter running in
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javascript. [yeah, expofiles would need some subset labelled as needing to
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be forcibly downloaded, but the rest coming only on demand.] Some django
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enthusiast must have done this already surely ? Ah yes, Brython.<br>
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<a href="https://github.com/brython-dev/brython">github.com/brython-dev/brython</a><br>
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<a href="https://www.brython.info/">www.brython.info</a>
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<p>
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Which is fun, but not useful. And not just because it is immature. None of
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this addresses <strong>our biggest problem: devising something that can be
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maintained by fewer, less-expert people who can only devote short snippets
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of time and not long-duration immersion</strong>.
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<h3>Our biggest problem</h3>
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We need:
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<ul>
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<li>something that can be maintained by fewer, less-expert people
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<li>who can only devote short snippets of time
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<li>without requiring weeks of long-duration deep immersion
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</ul>
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<h3>Federation of independent scripts</h3>
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<p>
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I know Wookey has been thinking of a loose federation of independent scripts
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working on the same data, but the more I look at troggle and the tasks it
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does the less I feel that would work. <strong>At the core there is a common data
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model that everything must understand</strong> - and the only unambiguous way of
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presenting that data model is working code, e.g. see
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<a href="http://expo.survex.com/handbook/troggle/trogarch.html">Troggle architecture</a> and click on the image
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to see a bigger copy. [It is out of date - if someone can quickly generate
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an update that would be nice. It's on my <a href="../computing/todo.html">to-do list..</a>] Much of what
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wallets.py does (originally by Martin Green) is in troggle already - but
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better. [There is a many:many relationship between svx files and wallet
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directories in reality, not 1:1]
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<p>
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<h3>troggle now</h3>
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Troggle is very nearly fully working (not with as many functions as
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originally envisaged admittedly) but very nearly [it is now: 8 July 2020].
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The QM data display needs writing; but other than that it's in pretty good
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shape. [Ah, yes, we should really add "drawings" as a core concept as well
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as "surveyscans". That will be a bit of work.]
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<p>
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<h3>Need for separate data-import checking scripts</h3>
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The one thing external scripts would be really useful for is syntax checking
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and reference checking prior to import. I have found some weird and
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wonderful filename paths inside the tunnel and therion drawings, and in
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survex *ref paths.
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<h3>Non-django troggle</h3>
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<p>Another possibility is ripping django out of troggle and leaving bare python
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plus a SQL database [see <a href="trog2030.html">Trog2030 proposal</a>]. This means that programmers would need to understand more SQL but would not need to understand "django". Arguably this
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could mean that we could gain.
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<p>Writing our own multi-user code would not be sensible, hence the database.
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But we could move to a read-only system where the only writing happens on data-import.
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Then we could use python 'pickle()' or 'json()' read-only data structures, but we
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would need to create all our own indexing and cross-referencing code (which is <a href="#mud">a much bigger job</a><sup>*</sup> than you might think).
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<p>There would be more lower-level code, but the
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different segments of the system could be in caving-sensible modules not
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django-meaningful modules. And we would not have all the extra
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language-like constructs that django introduces e.g. <var>X.objects.set_all()</var>, which
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modern editors complain about because it is a django idiom and
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not a function within the python codebase.
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(We could retain an HTML templating engine though.)
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<h3><em>Addendum</em></h3>
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<p>There is a templating engine <a href="https://mozilla.github.io/nunjucks/">Nunjucks</a>
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which is a port to JavaScript of the Django templating system we use
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(via <a href="https://palletsprojects.com/p/jinja/">Jinja</a> - these are the same people who do Flask). This would be an obvious thing to use if we needed to go in that direction.
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<p>We need a templating engine because so much of the troggle coorindation output is in tables of data from diffrerent sources, e.g. see <a href=/survexfile/264">all survey data for 264</a>.
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<p>Several organisations have moved their user-interface layer to the browser using
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Nunjucks including <a href="https://service-manual.nhs.uk/design-system/prototyping">
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the NHS digital service</a> and Firefox.
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<h3 =id="mud">* Later Note on object dependencies</h3>
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<!-- Philip Sargent 29 July 2020 -->
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<a href="http://picocontainer.com/inversion-of-control-history.html#timelines">
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<img class="onright" src ="../computing/ioc-timeline.png" width="200px"></a>
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<p>Currently every troggle code operation uses the django ORM <var>search</var> and <var>filter</var> operations on the central database to find any object it needs. If we don't have a central database then we have to use direct object references and we need to think about the design of <a href="https://medium.com/@geoffreykoh/implementing-the-factory-pattern-via-dynamic-registry-and-python-decorators-479fc1537bbe">a central registry object</a> to hold these. There is a well-studied design pattern that describes this design "<a href="http://www.laputan.org/mud/">Big Ball of Mud</a>" which and the contributing actions "Piecemeal growth" and "Sweeping it under the rug".
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<p>We are always using one object, e.g. a wallet, just to get at another object, e.g. a scan of some original notes, in order to check the data we are checking, e.g. a survex file. Maintaining two-way dependencies amoung all the objects is what "foreign keys" do in a database, but the problem doesn't go away when we don't have a database: it gets slightly harder. <p>One thing that is easier with troggle is that we don't have many object lifecycle issues. Everything is created once and lasts forever. There are only a few ephemeral objects during the initial data import from files.
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<h4>Wiring-up components</h4>
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<p>Troggle today doesn't need anything complex, a single <a href="https://hub.packtpub.com/python-design-patterns-depth-singleton-pattern/">registry
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singleton</a> would probably be fine (though hard to test), but if it evolves towards being a set of interacting services then a more sophisticated architecture would be needed.
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<p>The Java community found "dependency resolution" very helpful for wiring-up loosely objects/components in the late 1990s with the "<a href="http://picocontainer.com/inversion-of-control.html">Inversion of Control</a>" technique which can be implemented in several ways, most commonly using "<a href="https://martinfowler.com/articles/injection.html">Dependency Injection</a>". But for troggle we must be careful that doing this the "right" way may make the code even more inaccessible to novice caver-programmers than django is. Which is the whole point of moving away from django. Fortunately python programmers have produced some recent guidance: <a href="https://blog.benpri.me/blog/2020/05/13/python-dependency-injection-made-simple/">Python Dependency Injection Made Simple</a> and <a href="https://python-dependency-injector.ets-labs.org/introduction/di_in_python.html">Dependency injection and inversion of control in Python</a>. We should probably use the simpler "<a href="http://picocontainer.com/constructor-injection.html">Constructor Injection</a>" variation as we need to make all our code <a href="http://picocontainer.com/mock-objects.html">more easily testable</a>. Flask uses that.
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<hr />
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Return to: <a href="trogdesign.html">Troggle design and future implementations</a><br />
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Return to: <a href="trogintro.html">Troggle intro</a><br />
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Troggle index:
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<a href="trogindex.html">Index of all troggle documents</a><br />
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<hr />
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</body>
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</html>
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