What is id?

An ID (short for identifier) is a unique label that a computer system assigns to an object-like a user, a file, a piece of data, or a running program-so it can be distinguished from everything else.

Let's break it down

  • Unique: No two items that share the same scope should have the same ID.
  • Simple format: IDs are often numbers (e.g., 12345) or short strings (e.g., “user_01”).
  • Scope matters: An ID must be unique only where it’s used-inside a single table, a single web page, or a single operating system process list.
  • Generated automatically: Many systems create IDs for you (auto‑increment in databases, UUID generators, OS process counters).

Why does it matter?

IDs let software quickly find, update, or delete the exact thing you’re interested in without confusion. They make data relationships possible (linking a comment to a user), enable security checks (verifying who you are), and keep large systems organized and fast.

Where is it used?

  • HTML: the id attribute tags a specific element so CSS or JavaScript can target it.
  • Databases: primary keys (numeric IDs or UUIDs) uniquely identify rows.
  • Operating systems: each running program gets a Process ID (PID).
  • APIs & services: user IDs, order IDs, session IDs, etc., travel between client and server.
  • File systems: inode numbers act as IDs for files on many Unix‑like systems.

Good things about it

  • Fast look‑ups: Searching by a simple ID is much quicker than scanning full records.
  • Clear relationships: IDs let you link data across tables or services cleanly.
  • Consistency: Once assigned, an ID never changes, so references stay reliable.
  • Scalability: Systems can handle millions of items when each has a compact, unique ID.

Not-so-good things

  • Collisions: If IDs aren’t truly unique, data can become corrupted or overwritten.
  • Predictability: Simple sequential IDs can expose how many records exist, which may be a security risk.
  • Over‑reliance: Storing too much meaning in an ID (e.g., encoding user type) can make future changes hard.
  • Management overhead: Generating globally unique IDs (like UUIDs) adds extra processing and storage cost.