Q.1 What are the data and functional requirements of grid computing? Explain the layered architecture of grid with a neat diagram? Data Requirement The data aspects of any Grid Computing environment must be able to effectively manage all aspects of data, including data location, data transfer, data access, and critical aspects of security. The core functional data requirements for Grid Computing applications are: 1. The ability to integrate multiple distributed, heterogeneous, and independently managed data sources. 2. The ability to provide efficient data transfer mechanisms and to provide data where the computation will take place for better scalability and efficiency. 3. The ability to provide data caching and/or replication mechanisms to minimize network traffic. 4. The ability to provide necessary data discovery mechanisms, which allow the user to find data based on characteristics of the data. 5. The capability to implement data encryption and integrity checks to ensure that data is transported across the network in a secure fashion. 6. The ability to provide the backup/restore mechanisms and policies necessary to prevent data loss and minimize unplanned downtime across the grid. Functional Requirements The core functional requirements for grid applications are: 1. The ability to allow for independent management of computing resources 2. The ability to provide mechanisms that can intelligently and transparently select computing resources capable of running a user's job 3. The understanding of the current and predicted loads on grid resources, resource availability, dynamic resource configuration, and provisioning 4. Failure detection and failover mechanisms 5. Ensure appropriate security mechanisms for secure resource management, access, and integrity The Semantic Grid can be divided into four service layers – base services, data services, information services and knowledge services. Base services This layer is primarily concerned with large-scale pooling of computational resources. The base services provided by this layer are related to resource discovery, allocation and monitoring, user authentication, task scheduling or co-scheduling and fault tolerance. Data services This layer mainly provides computationally intensive analysis of large-scale-shared data sets or databases, which could range in size from hundreds of terabytes to petabytes, across widely distributed scientific communities. The services provided by this layer are related to data storage, metadata management, data replication and data transfer. Information services This layer allows uniform access to heterogeneous information sources and provides commonly used services running on distributed computational resources. Uniform access to information sources relies on metadata to describe information and to help with integration of heterogeneous resources. The granularity of the offered services can vary from subroutine or method calls to complete applications. Hence, in scientific computing, services can include the availability of specialized numerical solvers, such as a matrix or partial differential equation solver, to complete scientific codes for applications such as weather forecasting and molecular or fluid dynamics. In commercial computing, services can be statistical routines based on existing libraries or predictive services that offer coarse-grained functionality, such as database profiling or visualization. Services in this layer can, therefore, be offered by individual providers or by corporations; they may be specialized for specific applications, such as genomic databases or general purpose, such as numerical libraries. Knowledge services

This layer focuses on knowledge representation and extraction. It provides services that can be used to search for patterns in existing data repositories, and the management of information services, e.g. it can provide knowledge discovery from a huge amount of data using a variety of data-mining mechanisms. It can provide semantic meaning of information services aggregated from the information services layer. This layer is domain-oriented such as bioinformatics, and usually uses domain knowledge built with its own ontology.

================================================================================== Q.2 Explain briefly about grid infrastructure. Differentiate Data Grid and Computation Grid? Grid infrastructure The grid infrastructure forms the core foundation for successful grid applications. This infrastructure is a complex combination of a number of capabilities and resources identified for the specific problem and environment being addressed. In initial stages of delivering any Grid Computing application infrastructure, the developers/service providers must consider the following questions in order to identify the core infrastructure support required for that environment: 1. What problem(s) are we trying to solve for the user? How do we address grid enablement simpler, while addressing the user's application simpler? How does the developer (programmatically) help the user to be able to quickly gain access and utilize the application to best fit their problem resolution needs? 2. How difficult is it to use the grid tool? Are grid developers providing a flexible environment for the intended user community? 3. Is there anything not yet considered that would make it easier for grid service providers to create tools for the grid, suitable for the problem domain? 4. What are the open standards, environments, and regulations grid service providers must address? In general, a Grid Computing infrastructure component must address several potentially complicated areas in many stages of the implementation. These areas are: •

Security

•

Resource management

•

Information services

•

Data management

Data Grid The requirement for key data forms a core underpinning of any Grid Computing environment. For example, in data-intensive grids, the focus is on the management of data, which is being held in a variety of data

storage facilities in geographically dispersed locations. These data sources can be databases, file systems, and storage devices. The grid systems must also be capable of providing data virtualization services to provide transparency for data access, integration, and processing. In addition to the above requirements, security and privacy requirements of all respective data in a grid system is quite complex. We can summarize the data requirements in the early grid solutions as follows: • The ability to discover data • The access to databases, utilizing meta-data and other attributes of the data • The provisioning of computing facilities for high-speed data movement • The capability to support flexible data access and data filtering capabilities As one begins to realize the importance of extreme high performance-related issues in a Grid Computing environment, it is recommended to store (or cache) data near to the computation, and to provide a common interface for data access and management. Computational Grid A computational Grid Computing environment consists of one or more hardware- and software-enabled environments that provide dependable, consistent, pervasive and inexpensive access to high-end computational capabilities. the computational grids change the perception on the utility and availability of the computer power. Thus the computational Grid Computing environment became a reality, which provides a demand-driven, reliable, powerful, and yet inexpensive computational power for its customers. ================================================================================== Q.3 Discuss briefly about organization building and using grid based solution to solve their computing data and network requirements? Computational grids have emerged as the next phase in distributed computing. They offer a degree of resource sharing that will surpass even the World Wide Web as they will not only change the way in which data is accessed but also how this data is produced, consumed and stored. Grid computing is basically taking a number of inexpensive personal computers and connecting them via a network to build a supercomputer which can utilize the idle processing time on each machine to carry out tasks that would have previously required an expensive mainframe. The notion is that computational grids will offer users the ability to simply plug into the network and make use of computing resources such as mass storage systems (MSS) and large processing capabilities which are available on a 24/7 basis. Grid offers following benefits to an organization 1. Acceleration of implementation time frames in order to intersect with the anticipated business end results. 2. Improved productivity and collaboration of virtual organizations and respective computing and data resources. 3. Allowing widely dispersed departments and business to create virtual organizations to share data and resources. Grid computing is used in following areas 1. Life Sciences 2. Financial services 3. Higher Education 4. Engineering Services 5. Government 6. Collaborative games source:http://www.bcs.org/content/ConWebDoc/3054 ================================================================================== Q.4 Write notes on organizations developing grid computing toolkits frameworks and Middleware solution? 1. Globus The Globus project is a multi-institutional research effort to create a basic infrastructure and high-level services for a computational grid. A computational grid is defined as hardware and software infrastructure that provides dependable, consistent, pervasive, and inexpensive access to high-end computational capabilities. They have now evolved into an infrastructure for resource sharing (hardware, software, applications, and so on) among heterogeneous virtual organizations. These grids enable high creativity by

increasing the average and peak computational performance available to important applications regardless of the spatial distribution of both resources and users. The details on Globus infrastructure provided in Figure are based on the latest release from Globus called Globus GT3. Globus provides layered software architecture with a low-level infrastructure to host high-level services defined for grid. These high-level serv ices are related to resource discovery, allocation, monitoring, management, security, data management, and access. The lower layer infrastructure (GT3 Core) provides a framework to host the high-level services. 2. Globus Resource Allocation Manager (GRAM) GRAM provides resource allocation, process creation, monitoring, and management services. GRAM simplifies the use of remote systems by providing a single standard interface for requesting and using remote system resources for the execution of “jobs.” A GT3 Information service provides information about grid resources, for use in resource discovery, selection, and optimization. • The Monitoring and Discovery Service (MDS) is an extensible grid information service that combines data discovery mechanisms with the Lightweight Directory Access Protocol (LDAP). The MDS provides a uniform framework for providing and accessing system configuration and status information such as computer server configuration, network status, or the locations of replicated datasets. The current GT3 framework merges the MDS with the XML data framework for better integration with existing Web services and OGSA. • The latest Globus Toolkit (GT3) is a java implementation of the OGSI specification. • Organizations Building and Using Grid-Based Solutions to Solve Computing, Data, and Network Requirements These organizations and individuals are the real users of Grid Computing. They are benefiting from resource sharing and virtualization. As of now these projects are mostly in the scientific areas. We will be discussing some of the major grid projects and. infrastructures around the world. In general, these grid users need: • • •

On-demand construction of virtual computing system with the capabilities to solve the problems at hand including scarcity of computing power, data storage, and real-time processing A provision for collaborative visualization of the results of the above process A dynamic construction of virtual organizations to solve certain specific problems at hand

3. United States Department of Energy: Science Grid (DOE) The DOE Science Grid aims to provide an advanced distributed computing infrastructure based on Grid Computing middleware and tools to enable a high degree of scalability in scientific computing. The vision is to revolutionize the use of computing in science by making the construction and use of large-scale systems of diverse resources as easy as using today’s desktop environments. The DOE Science Grid is an integrated and advanced infrastructure that delivers: • • •

Computing capacity adequate for the tasks- in hand Data capacity sufficient for scientific tasks with location independence and manageability

he following work is used by the DOE’s Particle Physics Data Grid, Earth Systems Grid, and Fusion Grid projects: • •

•

A resource monitoring and debugging infrastructure for managing these widely distributed resources Several DOE applications use this grid infrastructure including computational chemistry, ground water transport, climate modeling, bio informatics, and so on. 4. Commercial Organizations Building and Using Grid-Based Solutions In the last couple of years we have seen a tremendous commercial interest in Grid Computing solutions. These commercial aspects are centered on the concept of resource sharing and resource virtual ization principles.

Source:http://www.bituh.com/2012/04/18/12-a-how-are-grid-computing-organization-classifiedexplain-giving-examples-16/ ================================================================================== Q.5 Describe about the relation of grid architecture with other distributed technologies? 1. Relation of grid architecture with World Wide Web A number of open and ubiquitous technologies are defined for the World Wide Web (TCP, HTTP, SOAP, XML) that in turn makes the Web a suitable candidate for the construction of the virtual organizations. However, as of now, the Web is defined as a browser-server messaging exchange model, and lacks the more complex interaction models required for a realistic virtual organization.

As an example, some of these areas of concern include single- sign-on, delegation of authority, complex authentication mechanisms, and event correlation mechanisms. Once this browser-to-server interaction matures, the Web will be suitable for the construction of grid portals to support multiple virtual organizations. This will be possible because the basic platforms, fabric layers, and networking connectivity layers of technologies will remain the same. 2. Relation of grid architecture with Distributed Computing Systems The major distributed technologies including CORBA, J2EE, and DCOM are well suited for distributed computing applications; however, these do not provide a suitable platform for sharing of resources among the members of the virtual organization. Some of the notable drawbacks include resource discoveiy across virtual participants, collaborative and declarative dynamic construction of a virtual organization, and the scale factor involved in potential resource-sharing environments. Another major drawback in distributed computing systems involves the lack of interoperability among these technology protocols. Some of these distributed technologies have attracted considerable Grid Computing research attention toward the construction of grid systems, the most notable of which is Java JINI This system, JINI, is focused on a platform- independent infrastructure to deliver services and mobile code in order to enable easier interaction with clients through service discoveiy, negotiation, and leasing. Sources:http://www.bituh.com/2012/04/19/12bii-discuss-relationship-of-the-grid-architecture-to-theother-distributed-technologies-such-as-the-world-wide-web-and-distributed-computing-systems-8/ ================================================================================== Q.6 Define Simple Object Access Protocol (SOAP), Web Services Architecture (WSA), Web Service Description Language (WSDL)? SOAP SOAP is a simple and lightweight communication protocol for clients and servers to exchange messages in an XML format over a transport-level protocol SOAP message is encapsulated in an envelope that consists of the following four parts • Various namespaces are used by the SOAP message, typically these include xmlns:SOAP-ENV (SOAP Envelope), xmlns:xsi (XML Schema for Instance) and xmlns:xsd (XML Schema Definition). • A set of encoding rules for expressing instances of applicationdefined data types. • An optional header for carrying auxiliary information for authentication, transactions and payments. • The Body is the main payload of the message. When an RPC call is used in the SOAP message, the Body has a single element that contains the method name, arguments and a Uniform Resource Identifier (URI) of the service target address. In addition, the fault entry can be used to explain a failure. SOAP is independent of the underlying transport protocol, so SOAP messages can be carried over many transport-level protocols such as HTTP, FTP, SMTP or more sophisticated protocols such as Java RMI JRMP or CORBA IIOP. HTTP is the most commonly used protocol because it can normally pass firewalls. Since XML is a universal standard, clients and servers built on different platforms can communicate with SOAP.

Web Services Architecture There are two ways to view the web service architecture. • The first is to examine the individual roles of each web service actor. • The second is to examine the emerging web service protocol stack. Web Service Roles There are three major roles within the web service architecture: • Service provider: This is the provider of the web service. The service provider implements the service and makes it available on the Internet. • Service requestor This is any consumer of the web service. The requestor utilizes an existing web service by opening a network connection and sending an XML request. • Service registry This is a logically centralized directory of services. The registry provides a central place where developers can publish new services or find existing ones. It therefore serves as a centralized clearinghouse for companies and their services. Web Service Protocol Stack A second option for viewing the web service architecture is to examine the emerging web service protocol stack. The stack is still evolving, but currently has four main layers. • Service transport This layer is responsible for transporting messages between applications. Currently, this layer includes hypertext transfer protocol (HTTP), Simple Mail Transfer Protocol (SMTP), file transfer protocol (FTP), and newer protocols, such as Blocks Extensible Exchange Protocol (BEEP). • XML messaging

This layer is responsible for encoding messages in a common XML format so that messages can be understood at either end. Currently, this layer includes XML-RPC and SOAP. • Service description This layer is responsible for describing the public interface to a specific web service. Currently, service description is handled via the Web Service Description Language (WSDL). • Service discovery This layer is responsible for centralizing services into a common registry, and providing easy publish/find functionality. Currently, service discovery is handled via Universal Description, Discovery, and Integration (UDDI). As web services evolve, additional layers may be added, and additional technologies may be added to each layer. WSDL WSDL is an XML-based specification that is used to completely describe a Web service, e.g. what a service can do, where it resides and how to invoke it The common elements in WSDL, are explained below. Data types The data types part encloses data type definitions that are relevant for message exchanging. For maximum interoperability and platform neutrality, WSDL uses XML XSD as the default data type. This part is extensible, meaning that it can contain arbitrary subsidiary elements to allow general data types to be constructed. The XSD namespace can be used to define the data types in a message regardless of whether or not the resulting message exchanging format is actually XML, or the resulting XSD schema validates the particular wire format. The element defines the data elements of an operation in a service. Each message can consist of one or more parts. The parts are similar to the parameters of a function or method call in a traditional programming language. is the core part of a WSDL document. Similar to a Java interface or a C++ class, it defines a set of abstract operations provided by a service. Each operation uses messages defined in the element to describe its inputs and outputs. identifies a concrete protocol and data format for the operations and messages defined by a particular . There may be an arbitrary number of bindings for a given portType, i.e. a binding can be document-oriented or use RPC. SOAP over HTTP is the most commonly used mechanism for transmitting messages between a service client and a service itself. A defines an individual service endpoint by specifying a single address for a binding. A is a set of related ports. Ports within a service have the following relationship • None of the ports communicate with each other. • If a service has several ports that share a , but employ different bindings or addresses, these are alternative ports where the port provides semantically equivalent behaviour. This allows a consumer of a WSDL document to choose particular port(s) to communicate with, based on some criteria (such as a protocol or distance).

================================================================================== Q.7: What are the layers available in the OGSA architectural organization? What are the OGSA basic services? OGSA is a de facto standard for building the next generation of service-oriented Grid systems. The GGF is currently coordinating a worldwide effort to complete the OGSA specification. OGSA is based on Web services technologies, but with some extensions. OGSA extends Web services by introducing interfaces and conventions in three main areas. • First, there is a dynamic and potentially transient nature of services in a Grid environment, in which particular service instances may come and go as work is dispatched, as resources are configured and provisioned, and as system state changes. Therefore, Grid services need interfaces to manage their creation, destruction and life cycle management. • Second, there is state. Grid services can have attributes and data associated with them. This is similar in concept to the traditional structure of objects in object-oriented programming. Objects have behaviour and data. Likewise, Web services needed to be extended to support state data associated with Grid services. • Third, clients can subscribe their interests in services. Once there is any change in a service, the clients are notified. This is a call-back operation from services to clients. Grid applications can be built from OGSA compliant services. Services in OGSA are composed of two parts, OGSA platform and core services. The OGSA platform services are Grid-based services related to user authentication and authorization, fault tolerance, job submission, monitoring and data access. Services in OGSA The core services in OGSA mainly include service creation, destruction, life cycle management, service registration, discovery and notification. OGSA introduces Grid service interfaces such as GridService, Factory, Registration, HandleResolver and Notification to support its core services. OGSA introduces the concepts of service instance and service data associated with each Grid service to support transient and stateful Grid services. In addition, the notification model in OGSA allows services to notify subscribed clients about the events they are interested in. OGSA defines various aspects related to a Grid service, e.g. The features of Grid services, and what interfaces are needed; but it does not specify how these interfaces should be implemented. That is the task of OGSI, which is a technical specification to specify how to implement the core Grid services as defined in OGSA in the context of Web services, specifically WSDL. The OGSI specifies exactly what needs to be implemented to conform to OGSA. Therefore, a Grid services can be defined as an OGSI compliant Web service. An OGSA compliant service can be defined as any OGSI compliant service whose interface has been defined by OGSA to be a standard OGSA service interface.

================================================================================== Q.8 What are the two dimensions of stateful nature of web service? Compare and contrast Web service with Grid service? There are two dimensions to the stateful nature of a web service: 1. A service is maintaining its state information. These are normally classified as application state and in case of grid services it directly maps to the state of the resource 2. The intercation pattern between client and the service can be stateful. There are numereous architecture styles and programming models for definning these stateful interactions including BPEL4WS and REST. Similarities between Grid service and Web Service 1. Grid service and Web Service Both are Special forms of distributed computing 2. Grid service and Web Service Both typically deal with wide-area distributed computing 3. A Grid service is basically a Web service with some additions (to make it able to store state information persistently rather than transiently at the server beyond the lifetime of a single request) Contrast between Grid service and Web Service 1. Web Service conceived to share information while Grid Service conceived to share computing power and resources like disk storage databases and software applications (eg: EGEE) “Grid service = Grid computing + Web services” 2. Every Grid service “is a” Web services, but not every Web service “is a” Grid service 3. Grid Services extends web services by 1. stateful service 2. service instantiation 3. A base set of service capabilites, including discovery facilities 4. lifetime management ================================================================================== Q.9 What is Service instance semantics, Service data semantics? Mention the attributes of SDE? Service instance semantics A Grid service instance is an instantiation of a Grid service that can be dynamically created and explicitly destroyed. A Grid service that can create a service instance is called a service factory, a persistent service itself. A client can request a factory to create many service instances and multiple clients can access the same service instance. A user job submission can involve one or more Grid service instances, which are created from corresponding Grid service factories running on three nodes. The implementations of the three services are independent of location, platform and programming language. Service data semantics Each Grid service instance is also associated with service data, which is a collection of XML elements

encapsulated as Service Data Elements (SDE). Service data are used to describe information about a service instance and their run-time states. Unlike standard Web services, which are stateless, Grid services are stateful and can be introspected. A client can use the standard FindServiceData() method defined in the GridService portType for querying and retrieving service data associated with a Grid service registered in a registry, i.e. the service type; if it is a service instance, the GSH of the service instance; the location of a service factory; and the run-time states. A service factory can create many service instances, of which each has a Service Data Set. A Service Data Set can contain zero or multiple SDEs

Q.10 Mention the core components of GT3 core?

Host environment A hosting environment is a specific execution environment that defines not only the programming model and language, but also the development and debugging tools that can be used to implement Grid service Web services engine A Web services engine is responsible for SOAP message exchange between clients and services. GT3 currently uses the Apache Axis as its SOAP engine, which manages SOAP message exchange Grid services container A Grid services container runs on top of a Web services engine, and provides a run-time environment for hosting various services. The idea of using a container in GT3 is borrowed from the Enterprise JavaBeans (EJB) model, which uses containers to host various application or components with business logic. A GT3 container can be deployed into a range of hosting environments in order to overcome the heterogeneity of today’s Grid deployments. For example, a Grid service could be implemented as an enterprise B2B application serving a large number of concurrent users, as well as a lightweight entry point into a Grid scheduling system for batch submissions. If a service is developed to comply with a container interface contract, it can be deployed in all environments supported by the container. ================================================================================== Q.11 What are the features of grid service container? A Grid services container runs on top of a Web services engine, and provides a run-time environment for hosting various services. The idea of using a container in GT3 is borrowed from the Enterprise JavaBeans (EJB) model, which uses containers to host various application or components with business logic. A GT3 container can be deployed into a range of hosting environments in order to overcome the heterogeneity of today’s Grid deployments. For example, a Grid service could be implemented as an enterprise B2B application serving a large number of concurrent users, as well as a lightweight entry point into a Grid scheduling system for batch submissions. If a service is developed to comply with a container interface contract, it can be deployed in all environments supported by the container. Compared with Web services, there are three major functional areas covered by a Grid service container: • Lightweight service introspection and discovery supporting both pull and push information flows. • Dynamic deployment and soft-state management of stateful service instances that can be globally referenced using an extensible resolution scheme.

• A transport independent Grid Security Infrastructure (GSI) supporting credential delegation; message signing and encryption; as well as authorization. ================================================================================== 12. Write short notes on. a) Schedulers Grid scheduling is defined as the process of mapping Grid jobs to resources over multiple administrative domains. A Grid job can be split into many small tasks. The scheduler has the responsibility of selecting resources and scheduling jobs in such a way that the user and application requirements are met, in terms of overall execution time (throughput) and cost of the resources utilized. three scheduling paradigms 1. Centralized scheduling In a centralized scheduling environment, a central machine (node) acts as a resource manager to schedule jobs to all the surrounding nodes that are part of the environment. 2. Distributed scheduling there is no central scheduler responsible for managing all the jobs. Instead, distributed scheduling involves multiple localized schedulers, which interact with each other in order to dispatch jobs to the participating nodes. There are two mechanisms for a scheduler to communicate with other schedulers – direct or indirect communication. 3. Hierarchical scheduling A centralized scheduler interacts with local schedulers for job submission. The centralized scheduler is a kind of a meta-scheduler that dispatches submitted jobs to local schedulers. b) Resource broker Input :- one or more job request Action :- Select and submit job to most appropriate resources. Output: none 1. Contact GIIS server(s) to obtain a list of available clusters. 2. Contact each resource's GRIS for static for static and dynamic resource Information( hardware and software characteristics, current queue and load, etc.) 3. For each job :(a) Select the cluster to which the job will be submitted. i. Filter out clusters that do not fulfill the requirements on memory, disk space architecture etc, and clusters that the user are not authorize to use. ii. Estimate the Total Time to Delivery (TTD) for each remaining resource. iii. Select the cluster with the shortest predicted TTD. (b) Submit the job to the selected resource. (c) Release any reservation made to non selected clusters.

c) Resource Management of Grid Computing The goal of resource discovery is to identify a list of authenticated resources that are available for job submission. In order to cope with the dynamic nature of the Grid, a scheduler needs to have. some way of incorporating dynamic state information about the available resources into its decision-making process Once the list of possible target resources is known, the second phase of the scheduling process is to select those resources that best suit the constraints and conditions imposed by the user, such as CPU usage, RAM available or disk storage. The four systems have been widely used for Grid based resource management and job scheduling. Condor is a resource management and job scheduling system, a research project from University of Wisconsin–Madison. The SGE is a distributed resource management and scheduling system from Sun Microsystems that can be used to optimize the utilization of software and hardware resources in a UNIX-based computing environment. The SGE can be used to find a pool of idle resources and harnesses these resources; also it can be used for normal activities, such as managing and scheduling jobs onto the available resources The PBS is a resource management and scheduling system. It accepts batch jobs (shell scripts with control attributes), preserves and protects the job until it runs; it executes the job, and delivers the output back to the submitter The LSF is a resource management and workload scheduling system from Platform Computing Corporation. LSF utilizes computing resources that include desktops, servers and mainframes to ensure policy-driven, prioritized service levels for access to resources d) Load balancing The automation of a business process, in whole or part, during which documents, information or tasks are passed from one participant to another for action, according to a set of procedural rules A system that defines, creates and manages the execution of workflows through the use of software, running on one or more workflow engines, which is able to interpret the process definition, interact with workflow participants and, where required, invoke the use of information technology tools and applications.

e) Grid portals A Grid portal is a Web-based gateway that provides seamless access to a variety of backend resources. In general, a Grid portal provides end users with a customized view of software and hardware resources specific to their particular problem domain. It also provides a single point of access to Grid-based resources that they have been authorized to use. This will allow scientists or engineers to focus on their problem area by making the Grid a transparent extension of their desktop computing environment. Grid portal services 1. Authentication 2. Job management 3. Data transfer 4. Information services f) Service-Oriented Architecture (SOA) Service-oriented architecture (SOA) is an evolution of distributed computing based on the request/reply design paradigm for synchronous and asynchronous applications 1. SOA services have self-describing interfaces in platform-independent XML documents. Web Services Description Language (WSDL) is the standard used to describe the services.

2. SOA services communicate with messages formally defined via XML Schema (also called XSD). Communication among consumers and providers or services typically happens in heterogeneous environments, with little or no knowledge about the provider. Messages between services can be viewed as key business documents processed in an enterprise.

3. SOA services are maintained in the enterprise by a registry that acts as a directory listing. Applications can look up the services in the registry and invoke the service. Universal Description, Definition, and Integration (UDDI) is the standard used for service registry. 4. Each SOA service has a quality of service (QoS) associated with it. Some of the key QoS elements are security requirements, such as authentication and authorization, reliable messaging, and policies regarding who can invoke services. g) Grid security demands and solutions Grid security is based on what is known as the Grid Security Infrastructure (GSI), which is now a Global Grid

Forum (GGF) standard. GSI is a set of tools, libraries, and protocols used in Globus and other grid middleware, to allow users and applications to access resources securely. GSI is based on a Public Key Infrastructure, with certificate authorities and X.509 certificates. GSI provides: • A public-key system; • Mutual authentication through digital certificates; • Credential delegation and single sign-on.