Markup[1] is the process of adding notes to a text to incorporate additional information and is also known by the term annotation[1]. These notes can be addressed to oneself (this passage is important) or to collaborating parties (this should be rephrased or updated) or to machines as instructions for further processing. A markup language[2] is a set of rules that describes the type of annotation used in a document, such that multiple parties/machines can understand its meaning.
Course
Concept
Markup might be as old as writing on media. The image below shows the annotation of a handwritten manuscript by Isaac Newton[3] (1643 - 1727 AD), where he discarded passages and made corrections to existing text. The next one is a combination of handwritten notes and highlighted passages made by a so-called marker[4], the device where the name markup language originates from. The picture on the right might already be considered a type of markup language, in which each colour represents a certain meaning (yellow=person, blue=date, orange=location, e.g.) which is explained in the legend next to it. This ensures that other parties/machines can understand what is meant by the different colours/markup as well, which is exactly what a markup language is supposed to do.
From left to right: Annotation of handwritten text[5], annotation of printed text[6], a marker pen[7] and markup of digital text[8].
History
Markup is the mechanism used to realize the idea of Vannevar Bush.
... a provision whereby any item may be caused at will to select immediately and automatically another.
It is the method by which any piece of digital text can be singled out and annotated with information such that it can act as hyperlink.
The first markup language GML[9] (Generalized Markup Language) created in 1969 by Charles Goldfarb, Edward Mosher and Raymond Lorie, was however never developed with the intention to create hyperlinks. It originated from a project started by IBM (International Business Machines Corporation) to create a machine-readable document database that could be used for legal practice[10].
Just as the laws of Nature, the laws of Society generally outlast the lifetime of an individual.The first concern of Goldfarb and his team was therefore not aimed at "how information can be found", but how to make sure that the created content survives the ages. The sections below describe some key features from their original design report[11].
Separation of content and format
Separation of content and format is an idea originally posted by William Tunnicliffe in 1967[12]. A format is the shape, size, layout, or general organization of something. It refers to the structure in which information, media, or physical items are arranged and presented. Consider for example the items below.
From left to right: Stone tablet from the Late Roman-Byzantine era (circa 500 CE)[13], the Nash Papyrus (circa 200 BCE)[14], ink and pigments on parchment (circa 1400 CE)[15] and a printed paper book (circa 2000 CE)[16].
Although probably not immediately apparent, the primary content of all the physical objects above is the same: The ten commandments from the Holy Bible[17]. The key takeaway here, is that the content has not changed over a period of 2000 years. What changed is the media (stone, papyrus, parchment, paper) and the presentation of that content (flat lines, heavily illustrated, structured columns). If one would be able to separate the content from its format, one could create content that is stable over time.
In first instance that sounds "easier said than done". Traditional media like the ones depicted above, more or less force the creator to act like a painter. He first has to assess the size of his canvas and then think about how to fit the content within these boundaries (size of paper, stone tablet, etc.). This is fundamentally different from computers though. Files are stored on hard drives as bits and bytes. One needs a computer program in order to retrieve the file from the drive and present it to the user in a human interpretable format. By basic operating principle, that makes that content and format are already fundamentally separated: The way the content is stored, does not equal the way it is presented.
What GML realized is that it stays that way. A GML file contains annotated content only and does not include embedded instructions as how to format that content. This is in contrast to popular computer applications like Word[18] or Powerpoint[19] in which the user again acts like a painter and first decides on paper size, sheet ratio or page orientation and then tries to squeeze in the content. In case of GML, independent specialized applications can worry about how to fit the same content to a different output format. In the early days these were mainly printing applications, wondering how to best fit the content to a certain paper size (A3, A4, A5) or newspaper column. Early markup languages therefore mainly used markup to describe the structure of the document (this is a table of content, this is a title, chapter, paragraph, etc.) such that the specialized programs could decide where to best put the line and page breaks.
Nowadays, the separation of content and format has become even more important as the creator does no longer determine how his content is presented. It is the user that determines whether the website is viewed on a screen (mobile phone, tablet, HD television), narrated by some sort of audio application, fed to a braille interpreter or whatever other technology the future might bring!
By separating format from content, the author ensures that the created content can survive the momentarily popular way to access that content.
File format
As mentioned earlier, files are stored on hard drives as bits and bytes. Bits are binary entities that can only have a value of 1 or 0. These entities are normally grouped in sets of eight called a byte. Moving through all possible combinations (0000 0000, 0000 0001, 0000 0010, .. , 1111 1111), will reveal that there a total of 256 different combinations for a single byte. The question is now what those 256 possibilities should represent and this is determined by something called a file format: A specification of the specific way that information is stored in a file.
From left to right: Stone tablet from the Late Roman-Byzantine era (circa 500 CE)[13], the Nash Papyrus (circa 200 BCE)[14], ink and pigments on parchment (circa 1400 CE)[15] and a printed paper book (circa 2000 CE)[16].
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