last modified: 2017-07-31

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Definition of data

The English term "data" (1654) originates from “datum”, a Latin word for "a given".[1] "Data" is a single factual, a single entity, a single point of matter.

Using the word "data" to mean "transmittable and storable computer information" was first done in 1946. The expression "data processing" was first used in 1954.[2]

Thoughts: the etymology suggests that data is "a given". Can you question this?

Data represents either a single entity, or a collection of such entitities ("data points"). We can speak also of datasets instead of data (so a dataset is a collection of data points).


A date

A color

A grade

A relation of friendship

A sound

A hearbeat

A user input

A duration

A curriculum vitae

A picture

A longitude and latitude

A price

A number of friends

A temperature

A list of favorite movies




3 take aways from the examples

1. Think about data in a broad sense

Data is not just text and figures. You should train in thinking about data in a broader sense:

  • pictures are data

  • language is data (including slang, lip movements, etc.)

  • relations are data (you know individual A, you know individual B, but the relationship between A and B is data as well)

  • preferences, emotional states…​ are data

  • etc. There is no definitive list, you should train yourself looking at buisness situations and think: "where is the data?"

2. metadata is data, too

Metadata: this is some data describing some other data.


The bibliographical reference (1)
a book (2)
1 the metadata
2 the data

→ Data without metadata can be worthless (imagine a library without a library catalogue)

→ Metadata can be informative in its own right, as shown with the NSA scandal: [3]

The trouble with metadata

3. zoom in, zoom out

We should remember considering that a data point can be itself a collection of data points:

  • a person walking into a building is a data point.

  • however this person is itself a collection of data points: location data + network relations + subscriber status to services + etc.

So it is a good habit to wonder whether a data point can in fact be "unbundled" (spread into smaller data points / measurements)

Some essential vocabulary to discuss data


  • This is a digital medium (because it’s on screen as opposed to analogic, if we had printed the pic on paper)

  • The type of the data is textual + image

  • The text is formatted in plain text (meaning, no special formatting), as opposed to more structured data-interchange formats (check json or xml).

  • The encoding of the text is UTF-8. Encoding has to do with the issue: how to represent alphabets and signs from different languages in text? (not even mentioning emojis?). UTF-8 is an encoding which is one of the most universal.

  • The tweet is part of a list of tweets. The list represents the data structure of my dataset, it is the way my data is organized. There are many alternative data structures: arrays, sets, dics, maps…​

  • The tweet is stored as a picture (png file) on my hard disk. "png" is the file format. The data is persisted as a file on disk (could have been stored in a database instead).

Data presented as a table


Finally: data and size

Data sizes

1 bit

can store a binary value (yes / no, true / false…​)

8 bits

1 byte (or octet)

can store a single character

~ 1,000 bytes

1 kilobyte (kb)

Can store a paragraph of text

~ 1 million bytes

1 megabyte (Mb)

Can store a low res picture.

~ 1 billion bytes

1 gigabyte (Gb)

Can store a movie

~ 1 trillion bytes

1 terabyte (Tb)

Can store 1,000 movies. Size of commercial hard drives in 2017 is 2 Tb.

~ 1,000 trillion bytes

1 petabyte (Pb)

20 Pb = Google Maps in 2013

The end

Find references for this lesson, and other lessons, here.