What is the significance of the accompanying figure in SAP from an accounting standpoint?

When an ERP system is used, all transactions in all areas of a company, get posted in a central database. Each transaction that gets posted gets its own unique number, called a document number. This number allows quick access to the data. If you need to look up a transaction online, you do so by referencing the document number, which acts as an index to the appropriate database table entries.