eXtensible Markup Language • “deﬁnes a set of rules for encoding documents in a format that is both human-readable and machine-readable” • Widespread acceptance means many off-the- shelf tools, libraries and procedures.
to its subscribers • Filter event streams • Any node may provide additional services based on events received • Store in a database • Display on a web page • Perform a follow-up observation(!) http://www.skyalert.org/
is a query language for selecting nodes from an XML document. In addition, XPath may be used to compute values (e.g., strings, numbers, or Boolean values) from the content of an XML document” (Wikipedia) • Comet lets subscribers specify an XPath expression and only forward events for which it evaluates to true (or non-zero) • /*[local-name()="VOEvent" and @role!="test"] • //Who[AuthorIVORN="ivo://lofar.transients/"] • This is a Comet “special”, not an IVOA standard.
securely with Bob ? And sends half to Bob Alice can sign with her key. Bob can verify the signature. A signature guarantees the sender of the message had possession of Alice’s key. She generates a PGP “key” PGP is an internet standard (RFC 4880) with various free & commercial implementations.
bits which make up the message are unchanged <element>value</element><element2>value2</element2> <element>value</element> <element2>value2</element2> • What is the legitimate role of a broker or repository?