Hi, This is a crucial point with respect to which, a clarification from Boris would help. In the OMA specification of the Context Management (Publish/Subscribe) Service, Context Elements have a field called "EntityId". There are two interpretations of what this "EntityId" means. Depending on which one is the correct one, we need to adjust our definitions: a) "EntityId" is just a "key" or "identifier" of the Context Element (for instance, used as key in a RDBMS). This was the interpretation I give in my document, so I Just explained that a Data Element had an "EntityId" associated to it. b) "EntityId" is an id of an entity the Context Element provides some information about. So, for example, "EntityId" in a Context Element could be "MyVillage" and then, there could be several ContextElements describing aspects about "Prado Museum". For example, I may have a Context Element describing Location (with attributes latitude and altitude) while another Context Element may have Temperature (with attributes temperature, and time at which the temperature was measured). If a) is the right interpretation, Context Elements would just be a special case of Data Element and, therefore, they would have an "EntityId" associated to them. As simple as that. If b) is the right interpretation, then I believe that "EntityId" and "EntityType" would not make sense in Data Elements. I still believe that we should link an "Id" and "DataType" to Data Elements. Then Context Elements would "extend" Data Elements so that they also add "EntityId" and "EntityType". What is rather clear to me is that events are just things that wrap data/context and link a time to them. In this respect, it makes sense to talk about data events or context events if we want to precise when an event is linked to a data element or a context element. Feedback from Boris about what is the right interpretation (a) or b) above) would allow us to perform the next iteration in this definition. Best regards, -- Juanjo On 14/06/11 18:38, Guy Sharon wrote: Boris - wouldn't it be also true to be able to obtain context by associating data with entity? i.e. No need to go through an event to get to context? So something like this [cid:part1.05010609.09000806 at tid.es] Guy Sharon Manager Event-based Middleware & Solutions Group ________________________________ [cid:part2.07030402.08010907 at tid.es]<http://www.ibm.com/smarterplanet> Event-based Middleware & Solutions<http://www.haifa.il.ibm.com/dept/services/soms_ebs.html> 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<mailto:guysh at il.ibm.com> From: Moltchanov Boris <boris.moltchanov at telecomitalia.it><mailto:boris.moltchanov at telecomitalia.it> To: Juanjo Hierro <jhierro at tid.es><mailto:jhierro at tid.es>, "fiware-data at lists.fi-ware.eu"<mailto:fiware-data at lists.fi-ware.eu> <fiware-data at lists.fi-ware.eu><mailto:fiware-data at lists.fi-ware.eu> Date: 14/06/2011 18:51 Subject: Re: [Fiware-data] Tentative definition of basic concepts: data, context and events Sent by: fiware-data-bounces at lists.fi-ware.eu<mailto:fiware-data-bounces at lists.fi-ware.eu> ________________________________ Dear Juajo, I would put the event definition before the Context. As I’ve said during the last conf-call, the data (including everything related to numbers and values) is a most generic case where only number (value) is the must. Everything else (meta-data, types, etc.) is optional. Then we would have an event as data + time when happened (the object referred by the data is implicit therefore could be omitted). Then adding the subject or object (referenced entity) we obtain the context, which inherit legacy properties of both the data (value) and event (when happened) as must and adding another must – explicit object or subject (entity) making it the context. I hope I’ve succeeded to explain my point of view. Thank you. Best Regards, Boris From: fiware-data-bounces at lists.fi-ware.eu<mailto:fiware-data-bounces at lists.fi-ware.eu> [mailto:fiware-data-bounces at lists.fi-ware.eu] On Behalf Of Juanjo Hierro Sent: Tuesday, June 14, 2011 12:58 PM To: fiware-data at lists.fi-ware.eu<mailto:fiware-data at lists.fi-ware.eu> Subject: [Fiware-data] Tentative definition of basic concepts: data, context and events Dear all, As you know, one of the action points from our last confcall had to do with providing a tentative definition of basic concepts in our chapter like data, context and event. Please find the document I have produced on the matter at: https://forge.fi-ware.eu/docman/view.php/9/141/Notes+and+Thoughts+on+definition+of+data-context-event.doc Just in case you believe it would be more easy to run a discussion via email following this email, I have attached the text of this document below. Hope you find it useful. Your feedback is welcome. 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://www.fi-ware.eu/> (http://data.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. Any data element has an entity in any FI-WARE Instance and, as such, it has an associated EntityId which universally and unequivocally indentifies the data element among the whole set of existing data elements. The basic concepts introduced so far are represented in Figure 1. [cid:part3.01090101.04030306 at tid.es] Figure 1. Basic Model for Data A cornerstone concept in FI-WARE is that data elements are not tied to a specific format. They can be transferred as an XML document or in some sort of efficient binary representation and then be stored in a Relational Database or as entries in a noSQL data base like MongoDB. 3. Definition of Context Context in FI-WARE is represented through context elements. A context element is just a particular case of data element. However, 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. 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 defined as a data element to which a number of standard event object properties (similar to a header) are associated. 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 was created. The data element and the standard properties linked to an event are used to describe, as mentioned above, something that has happened or is contemplated as having happened in a given domain. A context event The relationship (or difference) of the terms data and event is continuously debated. One summary of the philosophical and technical aspects of such debates is included in the background section of [Grove 06] with several references to the different opinions and definitions. For the purpose of FI-WARE and in specifically of the Context and Data Management Generic Enablers, we need to distinguish between the semantic level and the technical level of such a relationship that FI-WARE wishes to adopt, communicate, through its interfaces, and implement. Semantically speaking, the term data subsumes the term event meaning that some data can be semantically interpreted as events. From a technical perspective data is the way information is communicated in FI-WARE and it needs to be explicitly or implicitly identified as an event object and vice versa for processing the data as event. ________________________________ Este mensaje se dirige exclusivamente a su destinatario. Puede consultar nuestra política de envío y recepción de correo electrónico en el enlace situado más abajo. This message is intended exclusively for its addressee. We only send and receive email on the basis of the terms set out at. http://www.tid.es/ES/PAGINAS/disclaimer.aspx Questo messaggio e i suoi allegati sono indirizzati esclusivamente alle persone indicate. La diffusione, copia o qualsiasi altra azione derivante dalla conoscenza di queste informazioni sono rigorosamente vietate. Qualora abbiate ricevuto questo documento per errore siete cortesemente pregati di darne immediata comunicazione al mittente e di provvedere alla sua distruzione, Grazie. This e-mail and any attachments is confidential and may contain privileged information intended for the addressee(s) only. Dissemination, copying, printing or use by anybody else is unauthorised. If you are not the intended recipient, please delete this message and any attachments and advise the sender by return e-mail, Thanks. [cid:part4.08030103.04000702 at tid.es]Rispetta l'ambiente. Non stampare questa mail se non è necessario. _______________________________________________ Fiware-data mailing list Fiware-data at lists.fi-ware.eu<mailto:Fiware-data at lists.fi-ware.eu> http://lists.fi-ware.eu/listinfo/fiware-data ________________________________ Este mensaje se dirige exclusivamente a su destinatario. Puede consultar nuestra política de envío y recepción de correo electrónico en el enlace situado más abajo. This message is intended exclusively for its addressee. 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