What is data?

Data can be stored on a hard drive, streamed through a network, or captured live through sensors such as video cameras and microphones. If we are sampling from physical phenomena, such as a video or sound recording, the space is continuous and effectively infinite. Once this space is sampled, that is digitalized, a finite subset of this space has been created and at least some minimal structure has been imposed on it. The data is on a hard drive, encoded in bits, given some attributes such as a name, creation date, and so on. Beyond this, if the data is to be made use of in an application, we need to ask, "how is the data organized and what kinds of queries does it efficiently support?"

When faced with an unseen dataset, the first phase is exploration. Data exploration involves examining the components and structure of data. How many samples does it contain, and how many dimensions are in each sample? What are the data types of each dimension? We should also get a feel for the...