An activity is the fundamental unit of work in an OGSA-DAI workflow. An activity executes a single well-defined and modular data-related operation (e.g. accessing a data resource, updating a data resource, transforming data, delivering data). Activities are an extensibility point in OGSA-DAI - application developers may develop their own.
The activity framework is the OGSA-DAI component which parses and validates OGSA-DAI workflows, creates instances of activity classes corresponding to the activities specified in the workflow, sets up input and output pipes, executes the workflow and builds a request status. The activity framework is used by the data request execution resource and is typically accessed via a data request execution service.
The activity manager (also termed the activity specification manager) is a component that manages the activities available to an OGSA-DAI server and the accessing of these from the OGSA-DAI persistence and configuration components (in particular an activity specification DAO). Activity managers are an extensibility point in OGSA-DAI - application developers may develop their own.
The activity specification DAO manages the persistence and configuration of activities known to an OGSA-DAI server. It is a layer which interacts with persistence media so shielding information about persistence media from the rest of an OGSA-DAI server. Activity specification DAOs are an extensibility point in OGSA-DAI - application developers may develop their own.
An asynchronous request is a request in which a data request execution service returns a request status to the client as soon as the workflow starts executing. Along with this will be the ID of a request resource which the client can use to monitor the request status.
A certificate is a data structure that contains information about some client including their public key, distinguished name - their name as it appears on the certificate - and other identification information. They are issued by CAs and, in a Web services or Grid environment, can be submitted by clients to services so the services can authenticate and authorize the clients. For more information see http://en.wikipedia.org/wiki/Digital_certificate.
A certification authority, or CA, is an organisation that issues digital security certificates for use by other parties in a Grid enviroment. A service provider can select the CAs it trusts and only accept connections from clients who provide certificates signed by the CAs they trust. For more information see http://en.wikipedia.org/wiki/Certificate_authority.
The common components configuration DAO manages the persistence and configuration of the configuration of common OGSA-DAI components. It is a layer which interacts with persistence media so shielding information about persistence media from the rest of an OGSA-DAI server. Common components configuration DAOs are an extensibility point in OGSA-DAI - application developers may develop their own.
The common components configuration manager is a component that manages the configuration of common OGSA-DAI components and the accessing of this configuration from the OGSA-DAI persistence and configuration components (in particular a common components configuration DAO). Common components configuration managers are an extensibility point in OGSA-DAI - application developers may develop their own.
The OGSA-DAI context is a component on the OGSA-DAI server which serves as a repository for all the main OGSA-DAI core components including the resource manager, activity specification manager, common components configuration manager, persistence manager, login providers and application-specific activities and components.
A data access object, or DAO, is an object that manages the access to or storage of data in some application. It encapsulates knowledge of the data storage resource and hides data storage-specifics from the rest of the application. Data Access Object is a core J2EE design pattern - http://java.sun.com/blueprints/corej2eepatterns/Patterns/DataAccessObject.html. For more information see also http://en.wikipedia.org/wiki/Data_Access_Object.
A data request execution resource, or DRER, accepts requests from clients, executes these and possibly returns results. A DRER is associated with 0 or more OGSA-DAI data resources. A DRER can be viewed as a workflow management and execution resource.
A Data Request Execution Service, or DRES, is a Web service that allows access to the properties of a DRER and also allows clients to submit requests to the DRER.
A data resource is an OGSA-DAI abstraction of a database or other type of data resource. It manages interactions with the database for OGSA-DAI, in particular for any activities that perform interactions with databases, e.g. SQLQuery, XPathQuery or ListDirectory. Data resources are an extensibility point in OGSA-DAI - application developers may develop their own.
A data resource information service, or DRIS, is a Web service that allows access to the properties of an management of the lifetime of an OGSA-DAI data resource.
A data sink is an OGSA-DAI resource which allows clients to push data to an OGSA-DAI server. Data sinks are one way in which OGSA-DAI supports asynchronous data transfer.
A data sink service is a Web service that allows access to the properties of and management of the lifetime of an OGSA-DAI data sink. It also allows clients to push data into a data sink.
A data source is an OGSA-DAI resource which allows clients to pull data from an OGSA-DAI server. Data sources are one way in which OGSA-DAI supports asynchronous data transfer.
A data source service is a Web service that allows access to the properties of and management of the lifetime of an OGSA-DAI data source. It also allows clients to pull data from a data source.
A distinguished name is the name of the holder of a certificate as it appears on that certificate.
Grid Security Infrastructure, or GSI, is a security infrastructure for Grids and is supported by the Globus Toolkit. For more information see http://en.wikipedia.org/wiki/Grid_Security_Infrastructure.
A list is the name used by OGSA-DAI to refer to a block of data that is a list of other blocks delimited by special start and end of list markers (which are in themselves blocks).
A login provider is an OGSA-DAI component that takes an OGSA-DAI security context and returns a database login (which consists of a database username and password). They can be used, for example, to map distinguished names from certificates to database logins. Login providers are an extensibility point in OGSA-DAI - application developers may develop their own which perform application-specific mappings and may assume the use of application-specific security contexts.
A message layer security, or MLS, is an end-to-end security protocol which supports message encryption (to prevent eavesdropping) and message integrity (to prevent tampering). Message security is independent of the underlying transport protocol.
A MetadataWrapper is an OGSA-DAI wrapper for any object to be treated as meta-data. It allows application-specific meta-data to be used within OGSA-DAI. It is up to individual activities how they handle MetadataWrappers.
The OGSA-DAI server is just the term used to describe any deployment of OGSA-DAI e.g. a deployment of OGSA-DAI Axis onto Tomcat or OGSA-DAI GT onto Globus Toolkit/Tomcat. An OGSA-DAI server will contain one or more OGSA-DAI resources. How the server exposes these resources to clients is specific to the distribution of OGSA-DAI deployed. The most common OGSA-DAI distributions (e.g. OGSA-DAI Axis and OGSA-DAI GT) expose resources via WSRF-compliant Web services.
OGSA-DAI Axis is the name given to OGSA-DAI distributions compliant with Apache Axis.
OGSA-DAI GT is the name given to OGSA-DAI distributions compliant with Globus Toolkit Web Services Core.
The Open Grid Services Architecture - Data Access and Integration, or OGSA-DAI, is the name of both the database access and integration middleware whose documentation you are currently reading and the project that produces this middleware.
A parallel workflow is a set of sub-workflows executed in parallel.
The persistence manager is a component that manages the persistence and configuration of OGSA-DAI components. It provides access to a resource state DAO, an activity specification DAO and a common components configuration DAO. Persistence managers are an extensibility point in OGSA-DAI - application developers may develop their own e.g. to replace the default file-based configuration and persistence with one based around a relational database.
A pipe is a buffer that connects the output of one activity to the input of another activity and through which blocks from from one activity to the next.
A pipeline, or pipeline workflow, is a sequence of connected activities that form a directed acyclic graph. The output of each activity is connected to the input of another activity in the pipeline. Each activity receives its input from another activity or via input literals (basically constant values provided along with the activity in a workflow).
A policy decision point is an authorization component which decides, on the basis of information collected by policy information points whether or not some client is authorized to perform some action and any conditions or constraints that may be imposed upon the execution of that action.
A policy information point is an authorization component which collects information about a client (for example their certificate and actions they wish to perform) which is required to decide whether to authorize the client to perform some action, which is the responsibility of a policy decision point.
An OGSA-DAI resource is an encapsulation of some facet of OGSA-DAI state and behaviour. The state is exposed to clients using resource properties. Resources can be dynamically created and can have an associated lifetime which clients may be able to change (depending upon the type of the resource).
An OGSA-DAI resource group is a type of OGSA-DAI data resource which just holds the IDs of other OGSA-DAI data resources.
A request is an OGSA-DAI workflow consisting of connected activities each of which may be targeted at an OGSA-DAI resource.
A request management service is a Web service that allows access to the properties of an management of the lifetime of an OGSA-DAI request resource. It can be used by clients to access, and poll, the request status of an asynchronous request.
A request resource is an OGSA-DAI resource that represents a request and holds its execution state. It is created by a DRER when a request is accepted (that is, starts executing or is queued for execution). Request resources support the management of asynchronous requests and provide access to the request status of the request.
A request status is a representation of the status of execution of an OGSA-DAI request by a DRER. This includes the execution status of each activity and, depending upon the request, data itself. A request status is accessible via a request resource.
The resource manager is a component that manages the resources available to and exposed by an OGSA-DAI server and the accessing of these from the OGSA-DAI persistence and configuration components (in particular a resource state DAO). Resource managers are an extensibility point in OGSA-DAI - application developers may develop their own.
Resource properties are the properties exposed by OGSA-DAI resources and which represent the state of a resource as exposed to a client. Resource properties in OGSA-DAI are modelled after those of WSRF.
The resource state DAO manages the persistence and configuration of resources known to an OGSA-DAI server. It is a layer which interacts with persistence media so shielding information about persistence media from the rest of an OGSA-DAI server. Resource state DAOs are an extensibility point in OGSA-DAI - application developers may develop their own.
A security context is an OGSA-DAI component that acts as an attribute store and stores an indexed collection of security-related values. Security contexts are an extensibility point in OGSA-DAI - application developers may develop their own which contain application-specific security information. Security contexts are also specific to the presentation layer in use.
A sequence workflow is a set of sub-workflows each executed in sequence. For example a sequence workflow could be defined with two sub-workflows, one to create a database table and the second to bulk load data into this table. The execution of the sequence workflow ensures that the second sub-workflow, loading the data, does not start until the first, creating the table, has completed.
A session is an OGSA-DAI resource which allows data and state to be used across multiple requests. State or data deposited during the execution of one OGSA-DAI request can be accessed and used in another.
A session management service is a Web service that allows access to the properties of an management of the lifetime of an OGSA-DAI session.
A sticky resource is one that cannot be persisted as it contains state that is non-serializable by a persistence layer. This is intended for future use when looking at using multiple JVMs in conjunction with OGSA-DAI servers. It is intended that the server would decide whether a resource is sticky or not based upon its state and resource properties.
A synchronous request is a request in which a data request execution service returns a request status to the client only when the associated workflow has completed execution.
A transient resource is one that is not persisted because the resource creator does not wish it to be so.
A transport layer security, or TLS, is an point-to-point security protocol which supports authentication, message encryption (to prevent eavesdropping) and message integrity (to prevent tampering). For more information see http://en.wikipedia.org/wiki/Transport_Layer_Security.
A tuple is OGSA-DAIs internal representation of a row of relational data. It consists of one element per column of the row.
WSRF, or Web Services Resouce Framework, is an OASIS Web services specification degining how to model, access and interact with stateful resources via Web services. Further information can be found at http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=wsrf and http://en.wikipedia.org/wiki/Web_Services_Resource_Framework.
A workflow is a collection of activities whose inputs and outputs are connected such that outputs from activities flow into inputs from other activities. See also Request.