Three-tier Framework

A three-tier Framework
A Digital Library is an evolving organisation which comes into existence thanks to a series of development steps bringing together all the necessary constituents. The three notions of ‘systems’ developed along the way form a three-tier framework: Digital Library, Digital Library System, and Digital Library Management System, each corresponding to three different levels of conceptualisation of the Digital Library universe. All three systems play a central yet distinct role in the digital library development process. The definitions below are provided to clarify their specific characteristics.

• Digital Library (DL)

A potentially virtual organisation, which comprehensively collects, manages and preserves for the long term rich digital content, offering its targeted user communities specialised functionality on that content, of defined quality and according to comprehensive codified policies.

• Digital Library System (DLS)

A deployed software system underpinned by a possibly distributed architecture providing all the facilities required by a specific Digital Library. Users interact with a Digital Library through the corresponding Digital Library System.

• Digital Library Management System (DLMS)

A generic software system which provides the appropriate software infrastructure both to produce and administer a Digital Library System incorporating the suite of facilities considered fundamental for Digital Libraries and to integrate additional software offering more refined, specialised or advanced facilities.

Although the concept of Digital Library is intended to capture an abstract system consisting of both physical and virtual components, the Digital Library System and the Digital Library Management System capture real software systems. For every Digital Library, there is a unique Digital Library System in operation, which might comprise any number of interconnected smaller Digital Library Systems, whereas all Digital Library Systems are based on a handful of Digital Library Management Systems. A Digital Library is therefore the abstract entity which ‘comes to into being’ thanks to the software system constituting the Digital Library System, while the Digital Library Management System is the software system which is conceived to support the lifecycle of one or more Digital Library Systems.

These concepts are not unique to a Digital Library as they underlie every type of information environment and system, from databases, the web and Wikipedia to hospital information and banking systems, and so forth. What sets digital libraries apart from these other systems are the specific characterisations given above. Content should be rich, annotated, preserved for the long term, user should be targeted communities, functionality should be specialised, quality should be measurable and policies should be comprehensive. While these characterisations are abstract and open to interpretation, precluding a precise formal definition, they provide conceptual benchmarks against which every system can be measured and compared, and for which boundaries can be defined based on the specifics of individual digital libraries.