I disagree with some of the comments Boris has on events. In particular... "An event is a particular case of the context element that does not have the EntityId and EntityType components" Why tie it to context - an event can stand on its own! - you may want to refer to the meaning of the event as some contextual information but it is not a must. I think we can live without this sentence We need to distinguish how we identify events vs. how we deal with events. The processing doesnt care how you identified an event from the origin (data element). I therefore think that we shouldnt event mention any context in the event definition section. The data elements can be identified as events if.... , the data element can be identified as context if... - sometimes the data element can be identified as both - thats all. Please see my comments here... Once we agree on the content I offer to go through this for correcting the English (and there will be a lot there) Guy Sharon Manager Event-based Middleware & Solutions Group Event-based Middleware & Solutions phone : +972 4 8296587 mobile : +972 54 6976417 address : IBM R&D Labs in Israel, Haifa University Campus, Mount Carmel, Haifa, 31905, Israel email : guysh at il.ibm.com From: Moltchanov Boris <boris.moltchanov at telecomitalia.it> To: Juanjo Hierro <jhierro at tid.es>, "fiware-data at lists.fi-ware.eu" <fiware-data at lists.fi-ware.eu> Date: 17/06/2011 03:18 Subject: Re: [Fiware-data] Revised description of basic concepts: data elements, context elements and events Sent by: fiware-data-bounces at lists.fi-ware.eu Dear Juanjo and rest of the Folk, Please find attached the document, which might be already included as a part of our FI-WARE spec. I, personally, agree with our thoughts that Juanjo has expressed and have just tailored the below text to a specification style, excluding eventual verbosity (and somewhere correcting English, however I don?t pretend here). If you agree we may already use it as a part of official specification. I still need to improve the reference high-level pub/sub spec, not difficult job, however not sure if will have time. Let speak tomorrow morning. Best Regards, Boris From: fiware-data-bounces at lists.fi-ware.eu [ mailto:fiware-data-bounces at lists.fi-ware.eu] On Behalf Of Juanjo Hierro Sent: Thursday, June 16, 2011 8:29 PM To: fiware-data at lists.fi-ware.eu Subject: [Fiware-data] Revised description of basic concepts: data elements, context elements and events Folks, Please find enclosed a revised version of the document with the description of basic concepts: data elements, context elements and events. Hopefully it captures what I believe every of us have in mind. I will send later tonight some additional comments elaborating a little bit further some points. For your convenience and if it helps to continue discussion over the email, I attach below the text of the document as body of this message. Best regards, -- Juanjo 1. Motivation This document intends to provide a precise description of some basic concepts like data, context and events in FI-WARE. These concepts are fundamental in the description of the Data/Context Management platform in FI-WARE and the way applications are developed based on that platform. Contents of this document will be considered as baseline for a post to publish in our Data/Context Management blog in www.fi-ware.eu ( http://data.fi-ware.eu) 2. Definition of Data Data refers to information that is produced, generated, collected or observed that may be of relevance for processing, further analysis or information and knowledge generation. Essentially refers to information relevant to applications. Data in FI-WARE has associated a data type and a value. FI-WARE will support a set of built-in basic data types like in most programming languages. Values linked to these basic data types supported in FI-WARE are referred as basic data values. So we have the notion of the integer basic data type and basic values like ?2?, ?7? or ?365? that belong to the integer basic data type. A data element refers to data whose value is defined as a sequence of one or more <name, type, value> triplets referred as data element attributes, where the type and value of each attribute is either linked to a basic data type and a basic value or is linked to the data type and value of another data element. Note that each data element has an associated data type as any data in the system. This data type determines what concrete sequence of attributes characterizes that data element. There may be meta-data (also referred as semantic data) linked to attributes in a data element. However, existence of meta-data linked to a data element attribute is optional. Applications may assign an identifier to Data elements in order to store them in some Data Base. However, such identifier would be generated aside and would not be considered as part of the structure of the data element. Note that a given application may decide to use the value of some attribute linked to a data element as its identifier in a given data base but, again, there is no identifier associated to the representation of a data element. The basic concepts introduced so far are represented in Figure 1. Figure 1. Basic Model for Data A cornerstone concept in FI-WARE is that data elements are not tied to a specific format representation. They can be transferred as an XML document at some given point in time and then be translated into another XML document representation later on or be transformed into some sort of efficient binary representation as part of a message. They can be stored in a Relational Database, in a RDF Repository or as entries in a noSQL data base like MongoDB, adopting a particular storage format that may be the same or different to the format used when it is transferred. It should be possible to infer the data type associated to a given Data Element based on the XML document or the format of the message in which it is transferred (e.g., a specific element of the XML document if the same XML document type is used to represent data elements of different types or just the XML document type if a different XML document type is used per data type) or based on the structure used to store it (e.g., may be inferred from the name of the table in which the data element is stored). The way data elements are represented in memory by FI-WARE GEs is not specified. Therefore, the implementer of a FI-WARE GE may decide the way it represents data element in memory. 3. Definition of Context Context in FI-WARE is represented through context elements. A context element extends the concept of data element by associating an EntityId and EntityType to it, uniquely identifying the entity in the FI-WARE system to which the context element information refers. In other words, a context element is a data element to which we add the association to an EntityId and an EntityType. As an example, a measured temperature is a data element but in order to become a context element, has to refer to some entity which exhibits that temperature (a particular room, a particular building, etc). In addition, there may be some attributes as well as meta-data associated to attributes that we may define as mandatory for any type of context element in FI-WARE. The basic concepts behind context elements representation are represented in Figure 2. Figure 2. Basic Model for Context Note that similar statements regarding format representation of data elements also apply to context elements. 4. Definition of Event An event is an occurrence within a particular system or domain; it is something that has happened, or is contemplated as having happened in that domain. The word event object is used to mean a programming entity that represents such an occurrence (event) in a computing system [EPIA]. Events are represented as event objects within computing systems to distinguish them from other types of objects and to perform operations on them, also known as event processing. It is common to refer to event objects simply as events. In FI-WARE, event objects are created internally to some GEs like the Complex Event Processing GE or the Publish/Subscribe Broker GE. These event objects are defined as a data element (or a context element) to which a number of standard event object properties (similar to a header) are associated internally to the GE. The concrete set of standard event object properties in FI-WARE is still to be defined but we may anticipate that one of these properties would be the time at which the event object is detected by the GE (arrives to the GE). There might be other properties which may be defined and tools will be provided enabling applications or admin users to assign values to those properties based on values of data element attributes (e.g., source of the event or actual creation time) or other characteristics of the data element (i.e., DataType) or the context element (i.e., EntityId and EntityType) wrapped by the event object. Data events refer to event objects handled by the CEP GE or the Publish/Subscribe Broker GE wrapping a data element, while context events refer to event objects handled by the CEP GE or the Publish/Subscribe Broker GE wrapping a context element. Este mensaje se dirige exclusivamente a su destinatario. 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