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Data Types, Sources, and Structure

Lesson 4: Data Types, Sources, and Structure

What kinds of data do analysts work with?

Type

Description

Examples

Common tools

StructuredConsistent rows and columnsSpreadsheets, database tablesExcel, SQL
Semi-structuredSome organisation, but fields can vary between recordsJSON events, XML, log filesPython, SQL with JSON functions
UnstructuredNo predefined formatFree text, images, audio, PDFsNLP tools, specialised libraries

Most entry-level analytics work uses structured data.

Common field types

Field type

Description

Example

Can you calculate with it?

Numeric (continuous)Measured quantityRevenue, weight, timeYes
Numeric (discrete)Counted quantityNumber of itemsYes
Categorical (nominal)Labels with no orderRegion, product categoryCount only
Categorical (ordinal)Labels with a natural orderLow / Medium / High; ratings 1–5Count, rank, sometimes median
Date / timePoints in timeOrder date, timestampYes, for durations and trends
BooleanTrue / falseIs_returning_customerCount, percentage
IdentifierUniquely labels a recordOrder ID, customer IDNo
  • Numbers may represent measurements (revenue) or labels (a product code).
  • A code like 00127 should not be treated as a quantity just because it contains digits. Storing it as a number would also drop the leading zeros.

Where does data come from?

Source

What it contains

Example

Transaction systemsOrders, payments, bookingsE-commerce database
CRM toolsCustomer contacts, leads, dealsSalesforce, HubSpot
Web / app analyticsPage views, events, sessionsGoogle Analytics, Mixpanel
SurveysOpinions and self-reported dataCustomer satisfaction forms
SpreadsheetsManual or exported dataBudget trackers
Application logsSystem events and errorsServer logs
Public datasetsOpen government or research dataCensus data, Kaggle datasets
APIsData fetched from other servicesWeather, exchange rates

Before using any source, check:

  • Owner – who maintains it and who can answer questions?
  • Update frequency – real-time, daily, monthly?
  • Definitions – what does each field mean?
  • Permissions – are you allowed to use it for this purpose?
  • Known gaps – missing periods, tracking changes, known errors?

Example

An order table:

order_id

order_date

customer_id

product_category

quantity

unit_price

region

100012026-07-01C204Books2350South
100022026-07-01C118Electronics14,999North

Column

Role

order_idIdentifies a record
order_dateSupports time-based analysis
customer_idLinks to the customers table
product_category, regionCategories for grouping
quantity, unit_priceSupport calculations (revenue = quantity × unit_price)

Data quality questions

Dimension

Question to ask

Example problem

CompletenessAre required values present?15% of rows have no region
ValidityDo values follow the rules?Negative quantities
ConsistencyAre values recorded the same way?"Chennai", "chennai", "CHN"
UniquenessAre records duplicated?The same order appears twice
TimelinessIs the data current enough?Data last refreshed three weeks ago
AccuracyDoes it match reality?Prices differ from the product catalogue

A date stored as text, a duplicated order, or inconsistent region names can all distort the result.

Key takeaways

  • Understand what each column means before calculating anything.
  • A field's meaning matters more than its appearance or storage format.
  • Always check quality across completeness, validity, consistency, uniqueness, timeliness, and accuracy.

Data Analytics Tutorial

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