Database
A database is an organized collection of data. A relational database, more restrictively, is a collection of schemas, tables, queries, reports, views, and other elements. Database designers typically organize the data to model aspects of reality in a way that supports processes requiring information, such as (for example) modelling the availability of rooms in hotels in a way that supports finding a hotel with vacancies.
System
A system is a regularly interacting or interdependent group of items forming an integrated whole. Every system is delineated by its spatial and temporal boundaries, surrounded and influenced by its environment, described by its structure and purpose and expressed in its functioning.
Programming
Asking for efficiency and adaptability in the same program is like asking for a beautiful and modest wife. Although beauty and modesty have been known to occur in the same woman, we'll probably have to settle for one or the other. At least that's better than neither.
Gerald M. Weinberg, The Psychology of Computer Programming (1971), Chapter 2, page 22
