This covers the applications and infrastructures linking systems and services. Aspects of technical interoperability include interface specifications, interconnection services, data integration services, data presentation and exchange, and secure communication protocols. A major obstacle to interoperability arises from legacy systems. Historically, applications and information systems in public administrations were developed in a bottom-up fashion, trying to solve domain-specific and local problems. This resulted in fragmented ICT islands which are difficult to interoperate. Due to the size of public administration and the fragmentation of ICT solutions, the plethora of legacy systems creates an additional interoperability barrier in the technical layer. Technical interoperability should be ensured, whenever possible, via the use of formal technical specifications. Source: The New EIF. https://ec.europa.eu/isa2/eif_en The new European Interoperability Framework (EIF) is part of the Communication (COM(2017)134) from the European Commission adopted on 23 March 2017. The framework gives specific guidance on how to set up interoperable digital public services.