style-guide.txt

.. _documentation-style-guide:

=========================================
Style Guide and Documentation Conventions
=========================================

.. default-domain:: mongodb

This document provides an overview of the style for the MongoDB
documentation stored in this repository. The overarching goal of this
style guide is to provide an accessible base style to ensure that our
documentation is easy to read, simple to use, and straightforward to
maintain.

For information regarding the MongoDB Manual organization, see
:ref:`documentation-organization`.

Document History
----------------

**2011-09-27**: Document created with a (very) rough list of style
guidelines, conventions, and questions.

**2012-01-12**: Document revised based on slight shifts in practice,
and as part of an effort of making it easier for people outside of the
documentation team to contribute to documentation.

**2012-03-21**: Merged in content from the Jargon, and cleaned up
style in light of recent experiences.

**2012-08-10**: Addition to the "Referencing" section.

**2013-02-07**: Migrated this document to the manual. Added "map-reduce"
terminology convention. Other edits.

**2013-11-15**: Added new table of preferred terms.

**2016-01-05**: Standardizing on 'embedded document'

Naming Conventions
------------------

This section contains guidelines on naming files, sections, documents,
and other document elements.

- File naming convention:

  - For Sphinx, all files should have a ``.txt`` extension.

  - Separate words in file names with hyphens (i.e. ``-``.)

  - For most documents, file names should have a terse one or two word
    name that describes the material covered in the document. Allow
    the path of the file within the document tree to add some of the
    required context/categorization. For example it's acceptable to
    have ``/core/sharding.rst`` and ``/administration/sharding.rst``.

  - For tutorials, the full title of the document should be in the
    file name. For example,
    ``/tutorial/replace-one-configuration-server-in-a-shard-cluster.rst``

- Phrase headlines and titles so users can determine what questions the
  text will answer, and material that will be addressed, without needing
  them to read the content. This shortens the amount of time that
  people spend looking for answers, and improves search/scanning and
  possibly "SEO."

- Prefer titles and headers in the form of "Using foo" over "How to Foo."

- When using target references (i.e. ``:ref:`` references in
  documents), use names that include enough context to be intelligible
  through all documentation. For example, use
  "``replica-set-secondary-only-node``" as opposed to
  "``secondary-only-node``". This makes the source more usable
  and easier to maintain.

Style Guide
-----------

This includes the typesetting and English grammatical conventions
that all documents in the manual should use. The goal
here is to choose good standards, that are clear, and have a stylistic
minimalism that does not interfere with or distract from the
content. A uniform style will improve user experience and minimize
the effect of a multi-authored document.

Spelling
~~~~~~~~

Use American spelling.

Punctuation
~~~~~~~~~~~

- Use the Oxford comma.

  Oxford commas are the commas in a list of things (e.g. "something,
  something else, and another thing") before the conjunction
  (e.g. "and" or "or.").

- Use a single space after terminal punctuation, such as periods.

- Place commas and periods inside quotation marks.

.. NOTE: The above bullet replaces the commented bullet below. American style
   refers only to quote marks and not to parenthesis. I consulted several sites,
   including this one: http://www.thepunctuationguide.com/british-versus-american-style.html

.. - Use "American style" punctuation when enclosing punctuation
     (i.e. parentheses, quotes, and similar) interacts with terminal
     punctuation (i.e. periods, commas, colons, and similar.) This rule
     dictates that the terminal punctuation always goes *within* the
     enclosing punctuation, even if the terminal punctuation affects the
     sentence/clause outside of the quote or parenthetical.

..   This is counter to the "logical style" which is default in British
     English, because its easier to be consistent and edit using this
     rule, and because the style of the documents tends towards American
     English.

.. NOTE This last paragraph in the bullet (below) uses an example we no longer do.
   We no longer put parens around literals.

..   The one exception is if a literal string or inline code snippet is
     enclosed in quotations or parenthesis, it may make sense to move a
     period or comma further away from the literal string to avoid
     copy-and-paste errors or other confusion. For example, in this case,
     "``cfg.members[0].priorty = 1``." is worse than
     "``cfg.members[0].priorty = 1``".

Headings
~~~~~~~~

Use title case for headings and document titles. Title case capitalizes the
first letter of the first, last, and all significant words.

Verbs
~~~~~

Verb tense and mood preferences, with examples:

- **Avoid** the first person. For example do not say, "We will begin
  the backup process by locking the database," or "I begin the backup
  process by locking my database instance."

- **Use** the second person. "If you need to back up your database,
  start by locking the database first." In practice, however, it's
  more concise to imply second person using the imperative, as in
  "Before initiating a backup, lock the database."

- When indicated, use the imperative mood. For example: "Back up your
  databases often" and "To prevent data loss, back up your databases."

- The future perfect is also useful in some cases. For example,
  "Creating disk snapshots without locking the database will lead to
  an invalid state."

- Avoid helper verbs, as possible, to increase clarity and
  concision. For example, attempt to avoid "this does foo" and "this
  will do foo" when possible. Use "does foo" over "will do foo" in
  situations where "this foos" is unacceptable.

Referencing
~~~~~~~~~~~

- To refer to future or planned functionality in MongoDB or a driver,
  *always* link to the Jira case. The Manual's ``conf.py`` provides
  an ``:issue:`` role that links directly to a Jira case
  (e.g. ``:issue:\`SERVER-9001\```).

- For non-object references (i.e. functions, operators, methods,
  database commands, settings) always reference only the first
  occurrence of the reference in a section. You should *always*
  reference objects, except in section headings.

- Structure references with the *why* first; the link second.

  For example, instead of this:

  Use the :doc:`/tutorial/convert-replica-set-to-replicated-shard-cluster`
  procedure if you have an existing replica set.

  Type this:

  To deploy a sharded cluster for an existing replica set, see
  :doc:`/tutorial/convert-replica-set-to-replicated-shard-cluster`.

General Formulations
~~~~~~~~~~~~~~~~~~~~

- Contractions are acceptable insofar as they are necessary to
  increase readability and flow. Avoid otherwise.

- Make lists grammatically correct.

  - Do not use a period after every item unless the list item
    completes the unfinished sentence before the list.

  - Use appropriate commas and conjunctions in the list items.

  - Typically begin a bulleted list with an introductory sentence or
    clause, with a colon or comma.

- The following terms are one word:

  - standalone
  - workflow

- Use "unavailable," "offline," or "unreachable" to refer to a
  ``mongod`` instance that cannot be accessed. Do not use the
  colloquialism "down."

- Always write out units (e.g. "megabytes") rather than using
  abbreviations (e.g. "MB".)

Structural Formulations
~~~~~~~~~~~~~~~~~~~~~~~

- There should be at least two headings at every nesting level. Within
  an "h2" block, there should be either: no "h3" blocks, 2 "h3"
  blocks, or more than 2 "h3" blocks.

- Section headers are in title case (capitalize first, last, and
  all important words) and should effectively describe the contents
  of the section. In a single document you should strive to have
  section titles that are not redundant and grammatically consistent
  with each other.

- Use paragraphs and paragraph breaks to increase clarity and
  flow. Avoid burying critical information in the middle of long
  paragraphs. Err on the side of shorter paragraphs.

- Prefer shorter sentences to longer sentences. Use complex
  formations only as a last resort, if at all (e.g. compound
  complex structures that require semi-colons).

- Avoid paragraphs that consist of single sentences as
  they often represent a sentence that has unintentionally become too
  complex or incomplete. However, sometimes such paragraphs are useful
  for emphasis, summary, or introductions.

  As a corollary, most sections should have multiple paragraphs.

- For longer lists and more complex lists, use bulleted items rather
  than integrating them inline into a sentence.

- Do not expect that the content of any example (inline or blocked)
  will be self explanatory. Even when it feels redundant, make sure
  that the function and use of every example is clearly described.

ReStructured Text and Typesetting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- Place spaces between nested parentheticals and elements in
  JavaScript examples. For example, prefer ``{ [ a, a, a ] }`` over
  ``{[a,a,a]}``.

- For underlines associated with headers in RST, use:

  - ``=`` for heading level 1 or h1s. Use underlines and overlines for
    document titles.
  - ``-`` for heading level 2 or h2s.
  - ``~`` for heading level 3 or h3s.
  - ````` for heading level 4 or h4s.

- Use hyphens (``-``) to indicate items of an ordered list.

- Place footnotes and other references, if you use them, at the end of
  a section rather than the end of a file.

  Use the footnote format that includes automatic numbering and a
  target name for ease of use. For instance a footnote tag may look
  like: ``[#note]_`` with the corresponding directive holding the
  body of the footnote that resembles the following: ``.. [#note]``.

  Do **not** include ``.. code-block:: [language]`` in footnotes.

- As it makes sense, use the ``.. code-block:: [language]`` form to
  insert literal blocks into the text. While the double colon,
  ``::``, is functional, the ``.. code-block:: [language]`` form makes the source easier to
  read and understand.

- For all mentions of referenced types (i.e. commands, operators,
  expressions, functions, statuses, etc.) use the reference types to
  ensure uniform formatting and cross-referencing.

Paths and Hostnames
~~~~~~~~~~~~~~~~~~~

- Use angle brackets to denote areas that users should input the relevant
  path, as in ``--dbpath <path>``.

- When including sample hostnames, use ``example.com``,
  ``example.net``, or ``example.org``, which are reserved for
  documentation purposes. See `RFC2606
  <http://tools.ietf.org/html/rfc2606>`_ and `RFC6761
  <http://tools.ietf.org/html/rfc6761>`_ for more information.

Jargon and Common Terms
-----------------------

.. list-table::
   :header-rows: 1
   :widths: 10, 20, 10, 60

   * - Preferred Term
     - Concept
     - Dispreferred Alternatives
     - Notes

   * - :term:`document`
     - A single, top-level object/record in a MongoDB collection.
     - record, object, row
     - Prefer document over object because of concerns about
       cross-driver language handling of objects. Reserve record for
       "allocation" of storage. Avoid "row," as possible.

   * - :term:`database`
     - A group of collections. Refers to a group of data files. This
       is the "logical" sense of the term "database."
     -
     - Avoid genericizing "database." Avoid using database to refer to
       a server process or a data set. This applies both to the
       datastoring contexts as well as other (related) operational
       contexts (command context, authentication/authorization
       context.)

   * - instance
     - A daemon process (e.g. :binary:`~bin.mongos` or :binary:`~bin.mongod`)
     - process (acceptable sometimes), node (never acceptable), server.
     - Avoid using instance, unless it modifies something
       specifically. Having a descriptor for a process/instance makes
       it possible to avoid needing to make mongod or mongos
       plural. Server and node are both vague and contextually
       difficult to disambiguate with regards to application servers
       and underlying hardware.

   * - :term:`field` name
     - The identifier of a value in a document.
     - key, column
     - Avoid introducing unrelated terms for a single field. In the
       documentation we've rarely had to discuss the identifier of a
       field, so the extra word here isn't burdensome.

   * - :term:`field`/value
     - The name/value pair that describes a unit of data in MongoDB.
     - key, slot, attribute
     - Use to emphasize the difference between the name of a field and
       its value For example, "_id" is the field and the default
       value is an ObjectId.

   * - value
     - The data content of a field.
     - data
     -

   * - MongoDB
     - A group of processes or a deployment that implements the MongoDB
       interface.
     - mongo, mongodb, cluster
     - Stylistic preference, mostly. In some cases it's useful to be
       able to refer generically to instances (that may be either
       :binary:`~bin.mongod` or :binary:`~bin.mongos`.)

   * - embedded document
     - An embedded or nested document within a document or an array.
     - nested document
     -

   * - :term:`map-reduce`
     - An operation performed by the mapReduce command.
     - mapReduce, map reduce, map/reduce
     - Avoid confusion with the command, shell helper, and driver
       interfaces. Makes it possible to discuss the operation
       generally.

   * - cluster
     - A sharded cluster.
     - grid, shard cluster, set, deployment
     - Cluster is a great word for a group of processes; however, it's
       important to avoid letting the term become generic. Do not use
       for any group of MongoDB processes or deployments.

   * - sharded cluster
     - A :term:`sharded cluster`.
     - shard cluster, cluster, sharded system
     -

   * - :term:`replica set`
     - A deployment of replicating :binary:`~bin.mongod` programs that
       provide redundancy and automatic failover.
     - set, replication deployment
     -

   * - deployment
     - A group of MongoDB processes, or a standalone :binary:`~bin.mongod`
       instance.
     - cluster, system
     - Typically in the form MongoDB deployment. Includes standalones,
       replica sets and sharded clusters.

   * - data set
     - The collection of physical databases provided by a MongoDB
       deployment.
     - database, data
     - Important to keep the distinction between the data provided by
       a mongod or a sharded cluster as distinct from each "database"
       (i.e. a logical database that refers to a group of collections
       stored in a single series of data files.)

   * - :term:`primary`
     - The only member of a replica set that can accept writes.
     - master
     - Avoid "primary member" construction.

   * - secondary
     - Read-only members of a replica set that apply operations from
       the primary's oplog.
     - slave
     - Accept "secondary member" as needed.

   * - primary shard
     - The shard in a cluster that's "primary" for a database.
     - primary
     - Avoid ambiguity with primary in the context of replica
       sets.

   * - range based sharding
     - Refers to sharding based on regular shard keys where the range
       is the value of the field(s) selected as the shard key.
     -
     -

   * - hash based sharding
     - Refers to sharding based on hashed shard keys where the range
       is the hashed value of the field selected as the shard key.
     -
     - Even though hashed sharding is based on ranges of hashes, the
       sequence of hashes aren't meaningful to users, and the
       range-based aspect of hashed shard keys is an implementation
       detail.

   * - sharding
     - Describes the practice of horizontal scaling or partitioning as
       implemented in sharded clusters.
     - partitioning, horizontal scaling
     - Only use the terms "partitioning" and "horizontal scaling" to
       describe what sharding does, and its operation. Don't refer to
       sharding as "the partitioning system."

   * - metadata
     - data about data
     - meta-data, meta data
     -

Database Systems and Processes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- To indicate the entire database system, use "MongoDB," not mongo or
  Mongo.

- To indicate the database process or a server instance, use ``mongod``
  or ``mongos``. Refer to these as "processes" or "instances." Reserve
  "database" for referring to a database structure, i.e., the structure
  that holds collections and refers to a group of files on disk.

Distributed System Terms
~~~~~~~~~~~~~~~~~~~~~~~~

- Refer to partitioned systems as "sharded clusters." Do not use
  shard clusters or sharded systems.

- Refer to configurations that run with replication as "replica sets" (or
  "master/slave deployments") rather than "clusters" or other variants.

Data Structure Terms
~~~~~~~~~~~~~~~~~~~~

- "document" refers to "rows" or "records" in a MongoDB
  database. Potential confusion with "JSON Documents."

  Do not refer to documents as "objects," because drivers (and
  MongoDB) do not preserve the order of fields when fetching data. If
  the order of objects matter, use an array.

- "field" refers to a "key" or "identifier" of data within a MongoDB
  document.

- "value" refers to the contents of a "field".

- "embedded document" describes a nested document.

Other Terms
~~~~~~~~~~~

- Use ``example.net`` (and ``.org`` or ``.com`` if needed) for all
  examples and samples.

- Hyphenate "map-reduce" in order to avoid ambiguous reference to the
  command name. Do not camel-case.

Notes on Specific Features
--------------------------

- Geo-Location

  #. While MongoDB *is capable* of storing coordinates in
     embedded documents, in practice, users should only store coordinates
     in arrays. (See: `DOCS-41 <https://jira.mongodb.org/browse/DOCS-41>`_.)