Introduction

A ledger is a special type of database.

In a database, data can be organised in any particular manner.

Whereas a ledger records ownership of particular assets. These assets are moved from one owner to another via transactions.

Examples of ledgers include:

• Currency ledgers operated by banks;
• Land registries usually operated by a government body; or
• distributed ledgers to track cryptocurrencies, operated by a group of pseudo-anonymous entities.

Historical Implementation

Historically, ledgers were held and updated by a single operator entity. Throughout the course we will refer to this type of ledger as a centralised ledger. A centralised ledger’s single operator would be responsible for:

• Allowing asset owners (and possibly others) to read the ledger;
• Allowing and authorising valid transactions to update the ledger; and
• Notifying any relevant party (e.g. regulators) about particular changes to the ledger.

Many years ago, all ledgers would have been paper based. Nowadays it is much more common to have digital ledgers. We will discuss the nuances between digital ledgers and distributed ledger technologies in the next sections.