The SIS only contains alerts on persons or objects falling under one of the following alert categories:
An SIS alert always consists of three parts: firstly a set of data for identifying the person or object, subject of the alert, secondly a statement why the person or object is sought and thirdly an instruction on the action to be taken when the person or object has been found.
The quality, accuracy and completeness of the data elements enabling identification are the key conditions for the success of the SIS. For alerts on persons the minimum data set is name, sex, a reference to the decision giving rise to the alert and the action to be taken. When available, photographs and fingerprints must be added in order to facilitate identification and to avoid mis-identification. The system also offers the possibility to add links between alerts (e.g.: between an alert on a person and a vehicle).
The SIS consists of three major components: a central system, national systems which may contain a synchronised copy of the central system and a communication infrastructure (network) between the central system and the national systems. An alert which is entered in the SIS in one state is transferred in real time to the central system. It then becomes available so that authorised users can query the alert on the basis of the entered data-elements.
Each state using the SIS is responsible for setting up, operating and maintaining its national system and its national SIRENE Bureau. The EU Agency for large-scale IT systems, eu-LISA, is responsible for the operational management of the central system and the communication infrastructure. The European Commission is responsible for the general oversight and evaluation of the system and for the adoption of implementing measures such as the rules for entering and searching data.