Grids Similar to clusters but processors are more loosely coupled, tend to be heterogeneous, and are not all in a central location. Can handle workloads similar to those on supercomputers, but grid computers connect over a network (Internet?) and supercomputers’ CPUs connect to a high-speed internal bus/network Problems are broken up into parts and distributed across multiple computers in the grid – less communication betw parts than in clusters. A Proposed Architecture for Grid Systems Fabric layer: interfaces to local resources at a specific site. Connectivity layer: protocols to support usage of multiple resources for a single application; e.g., access a remote resource or transfer data between resources; and protocols to provide security.Resource layer manages a single resource, using functions supplied by the connectivity layer.Collective layer: resource discovery, allocation, scheduling, etc .Applications: use the grid resources.The collective, connectivity and resource layers together form the middleware layer for a grid. Cloud Computing 1Provides scalable services as a utility over the Internet. 2Often built on a computer grid 3Users buy services from the cloud.Grid users may develop and run their own software4Cluster/grid/cloud distinctions blur at the edges! Distributed Information Systems 1Business-oriented 2Systems to make a number of separate network applications interoperable and build “enterprise-wide information systems”. 3Two types discussed here: .Transaction processing systems .Enterprise application integration (EAI). Transaction Processing Systems1Provide a highly structured client-server approach for database applications 2Transactions are the communication model 3Obey the ACID properties: Atomic: all or nothing Consistent: invariants are preserved.Isolated (serializable).Durable: committed operations can’t be undone. Transactions Transaction processing may be centralized (traditional client/server system) or distributed.A distributed database is one in which the data storage is distributed – connected to separate processors.Nested Transactions 1A nested transaction is a transaction within another transaction (a sub-transaction) Example: a transaction may ask for two things (e.g., airline reservation info + hotel info) which would spawn two nested transactions .2Primary transaction waits for the results. While children are active parent may only abort, commit, or spawn other children. Implementing Transactions 1Conceptually, private copy of all data 2Actually, usually based on logs 3Multiple sub-transactions – commit, abort.Durability is a characteristic of top-level transactions only 4Nested transactions are suitable for distributed systems.Transaction processing monitor may interface between client and multiple data bases. Enterprise Application Integration 1Less structured than transaction-based systems2EA components communicate directly. Enterprise applications are things like HR data, inventory programs, …May use different OSs, different DBs but need to interoperate sometimes.3Communication mechanisms 

to support this include CORBA, Remote Procedure Call (RPC) and Remote Method Invocation (RMI). Distributed Pervasive Systems1The first two types of systems are characterized by their stability: nodes and network connections are more or less fixed 2This type of system is likely to incorporate small, battery-powered, mobile devices 1Home systems2Electronic health care systems – patient monitoring 3Sensor networks – data collection, surveillance. Home System Built around one or more PCs, but can also include other electronic devices: 1Automatic control of lighting, sprinkler systems, alarm systems, etc. 2Network enabled appliances 3PDAs and smart phones, etc. Sensor Networks 1A collection of geographically distributed nodes consisting of a comm. device, a power source, some kind of sensor, a small processor… 2Purpose: to collectively monitor sensory data (temperature, sound, moisture etc.,) and transmit the data to a base station 3“smart environment” – the nodes may do some rudimentary processing of the data in addition to their communication responsibilities. Software Architectures – describe the organization and interaction of software components; focuses on logical organization of software (component interaction, etc.)System Architectures - describe the placement of software components on physical machines
The realization of an architecture may be centralized (most components located on a single machine), decentralized (most machines have approximately the same functionality), or hybrid (some combination).
Architectural Styles 1An architectural style describes a particular way to configure a collection of components and connectors. .Component - a module with well-defined interfaces; reusable, replaceable.Connector – communication link between modules2Architectures suitable for distributed syste***ayered architectures* Object-based architectures* Data-centered architectures.Event-based architectures. Data-Centered Architectures 1Main purpose: data access and update 2Processes interact by reading and modifying data in some shared repository (active or passive) Traditional data base (passive): responds to requests. Blackboard system (active): clients solve problems collaboratively; system updates clients when information changes. 3Another example: web-based distributed systems where communication is through web services (Ch 12). System Architectures for Distributed Systems Centralized: traditional client-server structure.Vertical (or hierarchichal) organization of communication and control paths (as in layered software architectures).Logical separation of functions into client (requesting process) and server (responder).Decentralized: peer-to-peer.Horizontal rather than hierarchical comm. and control .Communication paths are less structured; symmetric functionality .Hybrid: combine elements of C/S and P2P.Edge-server systems.Collaborative distributed systems.Classification of a system as centralized or decentralized refers to communication and control organization, primarily. Traditional Client-Server1Processes are 

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