7. Relevance of Documentation

A map is not the territory it represents, but, if correct, it has a similar structure to the territory, which accounts for its usefulness. If the map could be ideally correct, it would include, in a reduced scale, the map of the map; the map of the map, of the map; and so on, endlessly, a fact first noticed by Royce.

—Alfred Korzybski, Science and Sanity, Chapter IV, p. 58.

The relevance of documentation, \(R_{doc}\) deteriorates, whenever the source code is changed, but the documentation is not updated.

The rate of deterioriation for a given piece of documentation increases with

  • the distance to the source code, \(D_{source} \ge 0\)
  • the inavailability of a documentation editor, \(I_{edit} \ge 0\)
  • the necessary effort for synchronization with the master document, \(E_{sync} \ge 0\)
  • the inertia of the human components \(H_{inertia} \ge 1\) involved.

The likeliness of relevance of a given piece of documentation, \(L_{R_{doc}}\) is therefore:

(7.1)\[\begin{split}& L_{R_{doc}} = \left( \left( \frac{1 + ( {D_{source}} + {I_{edit}} + {E_{sync}} + {H_{inertia}} )}{2}\right)\cdot{H_{inertia}} \right)^{-1}\\\end{split}\]

7.1. Introduction

The relevance of documentation is a measure of how similar the structure of the documentation is to the structure of the source code.

This is closely connected to the map–territory relation of General semantics. A thorough understanding of this principle really helps manage the expectations of what documentation of source code is, is not and can be. The fact, that documentation can never be accurate in the sense of a bijective mapping, does not mean it can not be helpful – even essential – for a human brain to construct an appropriate model.


figure 7.1 I think they might be having sushi

A major problem of software documentation arises from the fact, that the documented source code is often not available to the reader. Imagine, being given the following instructions for obtaining an item from a certain location:

  • go straight
  • go left
  • look at the sign, that says “Menu”
  • order the second item
  • bring it back

However, you are only given access up to a fence with a locked gate, where you can see the straight part of the road and the left turn, but you cannot see the menu. At the locked gate, there is only a sign with yesterday’s menu. Now you are supposed to predict what the second item on today’s menu will be without being able to examine the actual menu (see figure 7.1). It is pretty obvious, that this cannot be reliably done, especially if the menu is changing daily to whatever the chef feels like.

This describes the situation developers often find themselves in when working with proprietary software. But even when source code access is available – since they are incidentally the developer, who works on it – they are still expected to produce documentation for people that cannot understand the code; i.e., these people – who may just as well be future versions of the developer himself – choose to stay at the fence and refuse to walk through the gate. So developers may write things like: “And then look around in the source code, to find out what the real state of affairs is at any given moment.” However, they cannot expect any particular reader to make the effort. See the Sphinx and Doxygen document generators in section 10, Sphinx Documentation Generator for excellent examples, how the entire source is included for cross-referencing[1].

So, how much interest can you muster for the utterly boring description of a treasure hunt for an unspecified treasure in a country you don’t know and don’t have the means to ever get to?

For me, that is one trivially self-evident answer to questions like “What’s with the aversion to documentation in the industry?”. The rapid deterioration of relevance for documentation during the development phase being another.

However, having no documentation at all is not a viable option and there are certainly ways to reduce the effort and increase the relevance of documentation.

7.2. Source and documentation management

Derived from the above equation, the best likeliness of relevance of a given piece of documentation is achieved when all deterioration factors, \({D_{source}}\), \({I_{edit}}\), \({E_{sync}}\), \({H_{inertia}}\) are at a minimum, which makes \(L_{R_{doc}} = 1\).

To discuss the likeliness of relevance of a given piece of documentation, it is necessary to define a model, which explains the parameters in their respective context (see figure 7.2).

figure 7.2 Source and documentation management


The required editor for a change is just one of a possible multitude of appropriate editors. It is not necessarily the preferred editor of a specific programmer (see figure 7.3).

figure 7.3 Guaranteed and preferred editors

7.3. Minimum Distance to Source Code

A distance to source code, \({D_{source}}\) of \(0\) corresponds to the principle “the source is the documentation”, i.e., there is no additional documentation for the source code. Substituting \({D_{source}}\) by \(0\) in equation (7.1) results in:

(7.2)\[\begin{split} & \left( \left( \frac{1 + ( {I_{edit}} + {E_{sync}} + {H_{inertia}} )}{2}\right)^{H_{inertia}} \right)^{-1}\\\end{split}\]

In this case, the source editor and the documentation editor are necessarily the same and therefore \({I_{edit}}\) can be eliminated from equation (7.2):

(7.3)\[\begin{split}& \left( \left( \frac{1 + ( {E_{sync}} {H_{inertia}} )}{2}\right)^{H_{inertia}} \right)^{-1}\\\end{split}\]

When the source code changes are made to the master source file, \({E_{sync}}\) is also \(0\), equation (7.3) is reduced to:

(7.4)\[\begin{split} & \left( \left( \frac{1 {H_{inertia}}}{2}\right)^{H_{inertia}} \right)^{-1}\\\end{split}\]

Without automatic documentation generators that have to be triggered manually, human inertia \({H_{inertia}}\) is \(1\) and equation (7.4) is reduced to \(1\):

(7.5)\[\begin{split}& \left( \left( \frac{1 + 1}{2}\right)^{1} \right)^{-1} = 1\\\end{split}\]

So it seems, that the only time, documentation is guaranteed to be entirely relevant, is if there is none. In all other cases, documentation and source strictly abide by the properties of the map–territory relation[2].

However, there are tools like grep(1), ctags(1), etags(1), cscope(1), even Sphinx and doxygen, also (reluctantly) IDEs like Eclipse, which extract meta-information from undocumented source code to provide hyper linking facilities, which is in itself an extremely useful part of any documentation.

Other Generators produce Nassi-Shneiderman diagrams (flowcharts, activity diagrams), dependency graphs, etc.

Therefore the principle “the source is the documentation” is actually not so blunt or ridiculous as it may sound at first.

However, since automatically generated documentation requires a compilation step that may require manual triggering, \({H_{inertia}}\) may quickly become a signifanct factor.

7.4. Inertia

In the eternal sunshine of the spotless mind, each relevant source modification triggers a documentation update (see figure 7.4).

figure 7.4 Sunny day documentation update

But this is only true, when no human components are involved in the process of deciding, whether a source change is relevant for a documentation update. And this can only be the case when no manually created documentation parts have to be maintained. An example for this is the initial documentation produced by generators like Sphinx and Doxygen.

However, there is usually a more or less complex update decision process involved, which potentially results in increases of \({I_{edit}}\) and human inertia \({H_{inertia}}\) (see figure 7.5).

figure 7.5 Rainy day documentation update

The decision process looks somewhat like the activity diagram in figure 7.6. Feel free to add an infinite number of excuses for not updating the documentation or postponing the update indefinitely.

figure 7.6 Documentation update decision

7.5. Single Editor for Source and Documentation

When the documentation editor is the same as the source editor, the decisions about using or installing a separate documentation editor are removed. Therefore the result “not possible” is no longer returned (see figure 7.7).

figure 7.7 Documentation update decision with single editor

Consequently, the state machine for editing sources is also reduced. The state “Increment Inavailability” is removed and therefore \({I_{edit}}\) is no longer incremented (see figure 7.8).

figure 7.8 Editing with single editor

Therefore \({I_{edit}}\) is always \(0\) and equation (7.1) is reduced to:

(7.6)\[\begin{split}& L_{R_{doc}} = ( 1 + ( {D_{source}} + {E_{sync}} )^{H_{inertia}} )^{-1}\\\end{split}\]


Please, note, that in addition to a documentation editor, there may be separate documentation generators required to produce some form of final documentation (e.g., SVG, PNG, JPEG, HTML, PDF). However, the lack of these does not contribute to the deterioration of relevance, as long as the documentation source is updated.

If it is found, that the update of a piece of documentation without a visual representation created by the documentation generator is not possible, this decision may have to be revisited.

7.6. Synchronization

When there is a single file on just one computer, there is oviously no synchronization necessary and therefore \(E_{sync} = 0\).

Sometimes it is better to copy a project directory and work on the copy so that others are not disturbed by the intermediate states of development. That is called a branch or working on a branch. The original project file is the master.

As long as nothing leaves the branch directory, the documentation is not affected by the effort necessary for synchronizing the branch with the master. It is only, when e.g. a binary version from the branch is delivered to a production system, that the master documentation becomes less relevant until the branch with all documentation changes is synchronized (merged) with the master. This is the situation when \(E_{sync}\) becomes \(> 0\).

Human forgetfulness and general sloppiness are major factor for discrepancies, where branches are left to rot on flash drives and, newer versions are overwritten by older versions, etc.

This is why the process is nowadays highly automated by distributed version control systems (DVC).

DVCs are quite good, but sometimes you don’t want to check in changes, that need some final touch. In that case, you are back to copy or remote copy (scp(1), rsync(1)). So all other stages are still useful:

  • backup file
  • diff(1), patch(1), diff3(1)
  • scp(1), rsync(1)
  • VCS
  • DVCS

7.6.1. qs-gen-sync.pl (.sync.rc)

There are two aliases for backup and restore:

./sync.sh --backup send stuff from remote host
./sync.sh --restore get stuff from remote host

Generate initial .sync.rc:

isy -n

7.6.2. diff3

|:todo:| finish description of diff3(1)

diff3 doc/index.rst README.txt doc/overview.rst

7.7. Battling Human Inertia

The only way to defeat human inertia, \({H_{inertia}}\), is automation.

See also figure 7.9

|:todo:| finish description of scripting sh(1), make(1)

  • make/scripts are memory banks for knowledge


Source: Another way to think about geeks and repetitive tasks - Jon Udell

figure 7.9 Geeks and repetitive tasks

7.7.1. Integrated Development Environment

An IDE strives to be an integrated solution for cross-referencing, build automation, generated documentation.

In that sense, emacs(1) can also be classified as an IDE.

Eclipse is ridiculously hard to extend out of the box with plug-ins written in Java. E.g., in a forum question from 2016 about how to extend the default Java editor, somebody just wants to add a few keywords to the Java editor and gets links to a PDF slideshow about JDT and to Xtext. Neither are anywhere near trivial.

EASE does provide integration of script engines into Eclipse giving access to the workbench. This engine may be able to handle couple of keywords, if it can be added to Eclipse extension points (hooks), which needs to be researched |:todo:|. So in 2017 eclipse announces another convoluted overstructured object oriented integration, which still does not reach easily into an editing buffer (see also Internal and External Editors).

See also https://stackoverflow.com/questions/26912785/eclipse-jdt-syntax-highlighting-of-constants from 2014, which is still unanswered. The answers in https://stackoverflow.com/questions/13802131/in-an-eclipse-plugin-how-can-i-programmatically-highlight-lines-of-codes-in-the, give a variety of strategies to follow, but none of the answers gives a step-by-step example.

Here is another failed attempt https://www.eclipse.org/forums/index.php/t/489221/ for adding some highlighting to the Eclipse editor.

All in all Eclipse has still not reached the efficient state of the art provided by emacs(1) for decades. emacs(1) can be extended ridiculously simple with a multitude of tools glued together by Elisp.

As discussed in the article Using Automation to Assist – not replace – Manual Testing, automating entire workflows is very much ineffective (see figure 7.10).


Source: Using Automation to Assist – not replace – Manual Testing

figure 7.10 Using Automation to assist

In that context, a tightly integrated IDE – like Eclipse or Visual Studio – is the ineffective attempt to provide an entirely automated workflow in a one-size-fits-all manner.

In contrast, the loosely integrated approach with emacs(1) and tools provides a framework for task automation which can adapt to a variety of workflows.

A monolithic IDE usually has a plethora of cryptic configuration settings to provide some sort of rudimentary flexibility (customization), whereas the tool based IDE allows full modification of each automation step down to the code level.

[1]Sphinx even includes the source code for the documentation itself. However, the map–territory relation still holds, since there is no description of the process that transforms the documentation source code into the final output.
[2]Considering that the source code of a program is itself a map of an executable, requiring a processor (interpreter) and possibly a compiler to produce another representation, there really is no simple escape from the map–territory relation.