Q.List some of the cloud-based services that you are using at present.

Every time you tap, swipe, buy, post, or simply carry a phone down the street, you leave a trace. Multiply your traces by billions of people and billions of machines, running day and night, and you get the torrent the world calls big data. To reason about big data sensibly, the first question is not how big it is but where it all comes from — because the source shapes what the data looks like and what it can tell us.

The major sources fall into a few recognisable families:

• Social media. Posts, comments, likes, shares, photos, and videos from platforms used by billions. This is human-generated content: rich in opinion and behaviour, but messy, unstructured, and in every language.
• Transactions. Every online purchase, card payment, bank transfer, ticket booking, and bill generates a record. Transactional data is comparatively tidy — amounts, dates, identifiers — and is the backbone of business analytics.
• Machines and sensors. Weather stations, traffic cameras, fitness bands, smart meters, GPS units, and industrial equipment emit readings continuously without any human involvement. The growth of the Internet of Things has made this one of the fastest-growing sources, streaming data around the clock.
• Web and server logs. Websites and apps quietly record which pages were visited, when, from where, and what was clicked. Individually dull, collectively these logs reveal how people actually behave online.
• Organisational records. Hospitals, schools, governments, and companies digitise records — patient histories, admission data, land records, customer databases — adding steady institutional streams to the flood.

Notice a useful dividing line running through the list: some data is produced by people expressing themselves (social media, reviews), some by people transacting (purchases, bookings), and some by machines observing (sensors, logs). Machine-generated data never sleeps, which is a large part of why the total volume keeps exploding.

Why should a commerce or humanities student care? Because each source is a lens on society. Transactions reveal what people buy, sensors reveal how cities move, social media reveals what people feel. Businesses combine these lenses to forecast demand; governments use them to plan transport and health services. Knowing where data originates is also the first step in judging it — asking who generated it, who collected it, and with what consent, which is where the ethics of big data begins.