Common Alerting Protocol

The Common Alerting Protocol (CAP) is a XML based format for information exchange for hazards / specials event alerting. This protocol is an open standard can be freely distributed and translated into any other languages. It is widely used by U.S. government agencies for its simplicity and suit for general purpose. The CAP is a single output consisting four components “alert”, “info”, “resource”, and “area.” Additional information can be added as extended information trough "tag" "/tag" statement.

The "alert" segment provides basic information about the current message: its purpose, its source and its status, as well as a unique identifier for the current message and links to any other, related messages. An "alert" segment may be used alone for message acknowledgements, cancellations or other system functions, but most "alert" segment will include at least one "info" segment.

The "info" segment describes an anticipated or actual events in terms of its urgency (time available to prepare), severity (intensity of impact) and certainty (confidence in the observation or prediction), as well as providing both categorical and textual descriptions of the subject event. It may also provide instructions for appropriate response by message recipients and various other details (hazard duration, technical parameters, contact information, links to additional information sources, etc.) Multiple "info" segments may be used to describe different parameters (e.g. for different probability or intensity “bands”) or to provide the information in multiple language.

The "resource" segment provides an optional reference to additional information related to the "info" segment within which it appears in the form of a digital asset such as an image or audio file.

The "area" segment describes a geographic area to which the "info" segment in which it appears applies. Textual and coded descriptions (such as postal codes) are supported, but the preferred representation use geospatial shapes (polygons and circles) and an altitude or altitude range, expressed in standard latitude / longitude / altitude terms in accordance with a specified geospatial datum. (OASSIS Open, 2010, p. 47)

OASSIS Open, (2010). OASIS Common Alerting Protocol Version 1.2. Retrieved from