1. New Kind of Logic The first step to approch this questions consists of a new definition of logic operators able to explain the richness of the events happened in the system. Let’s introduce the following table: Occurs when both e1 and e2 occur irrespective of their order 1)Occurs when e1 or e2 occur (logic or) 2)Occurs when e1 timestamp is less then e2 3)Occurs T-time later after occurrence of e 4)Occurs when e1 followed by e2 occur with no interleaving of e3 It appears necessary to give an answer to the subsequent questions: how does the system remember the happened events? how long does the system have to remember that e1 event has happened and wait for event e2? A Monitoring Subscription Language in the Framework of Distributed System De Bortoli N., Palmiero R., Tortone G., Department of Physic, Department of Mathematics University of Naples and INFN section of Naples Abstract The Grid technology is attracting much interest, involving hundreds of researchers and software engineers around the world. The characteristics of Grid demand the developing of a suitable monitoring system, able to obtain the significant information in order to make management decision and control system behaviour. In this paper we are going to analyze a formal declarative interpreted language for the description of monitoring events. A user expresses his interest in verifying certain events, for example he/she is interested in the occurring of subsequent composite events: e1:= 'workload for ten minutes >K', after e2:='number of active machine <y', so he/she subscribes the event e:= e1 after e2. This language, inspired to Generalized Event Monitoring Language (GEM)[1], allows high level subscriptions to be specified as composition of atomic subscriptions and integrates the concept of real time. The language allows to express many temporal constraints, which would have been very difficult to specify in distributed systems. The goal of our research project consists of three steps: 1) the description of subscriptions through the use of a formal language; 2) the translating of the problem in a XML frame, using XML metalanguage tools; 3) the integration of this new language, made 'ad-hoc', in monitoring services. Introduction The monitoring is the activity of collecting, presenting and measuring significant information asked from human observer or automatic system. In the same way Grid monitoring consists of measuring the resource-related parameters in order to analyze usage, to detect and to notify fault situations and user-defined events with the aim of building a behaviour model of a Grid system. The present research work is involved in the context of Grid Ice but it is independent from it. In details it regards notification service and the area of XML document filtering. Temporal costraints are fundamental in many activities concerning distributed systems. Another important question is the changing of monitoring requirements without stopping the system. In this paper we are going to model a new declarative interpreted language to explain monitoring events, available to generic user, without knowing XML subscription language. We are interested in expressing many temporal constraints, which would have been very difficult to specify in distributed systems. Events, subscriptions, notifications An event is an incident which happens during the life of a system. Primitive events regard the changing of only one characteristic of a monitored object, a composite event is a composition of the primitive ones. A generic event consists of a finite set of ordered n-ples (n=4) where each one is defined in the subsequent way: event:= {(name, type,value,tms),...,} Which means: type:= type chosen between predefined primitive types used in a programming language name:= name of the event value:= value, boolean or numerical tms:= time of events happening The given definition is the most frequently used in literature regarding events. An atomic event or a simple event is defined as a set containing only one element: (name, type, value, tms) Example: (integer, pressure, 2, 12:31), or equally: (integer, pressure=2, at 12:31) A subscription is defined as a finite set of n-ples and constraints on the values that these n-ple can assume. A subscription specifies the attributes and the binary operators on the assumed values: { (integer, pressure, x, *) | x >= 1.5 } In the previous case the user is interested in all events where name is pressure, type is integer with value greater than 1.5, published any time from emission of subscription. Observation: for many authors the definition of the event is equivalent to the definition of notification. In this work a notification is the information sent to one or more users to notify an event of his/her interest. The algebra The aim of this paragraph is to define the cover relation between set events and set subscriptions. Let’s define set E that contains all events produced by the system. Let’s define set S that contains all subscription subscribed by users. The subset of all events that satisfy the given subscription is contained in E. Let’s call it: E_{s}. An event covers a subscription when it satisfies the given subscription. The cover relation, defined on the set subscriptions, is a partial ordered relation. OperatorsEvent e1 &e2It happens if e1 and e2 occur e1|e2It happens if e1 or e2 occur e1; e2It happens if e1 occurs before e2 e + timeTIt happens a T-time after e has occurred {e1; e2} ! e3It happens if e1 occurs before e2 and e3 hasn’t happened Discovery ConsumersScheduler HTML XMLNotificationCharts Data aggregation and abstraction Persistent storage Conclusions During this year we are going to define the details (sintax, sintax categories, semantic...) of this new language. The notion of real­time has been integrated within the language, allowing the users to subscribe events depending on time points. We define the occurrence interval of a composite event as the period of time during which it is occurring. We think that the language has to be: declarative: it previews sequences like event-action interpreted: so as to be portable generalised: to explain all kind of events user frendly: it has to be simple to use Our interest is also oriented towards real time logic. At the end of the research work we will develop a first version of the interpreter.