Data transformation steps are independent programs

This preview shows page 140 - 150 out of 173 pages.

Data transformation steps are independent programs. Each step completes before the next one begins. The output of each process must be saved to a temporary file, which is then read by the next process. A typical use is transaction processing in financial systems.
Assessment of batch sequential architectures Advantages Allows one to understand and reasons about the system in terms of process steps. Relatively easy to maintain (add, replace components). Disadvantages Not good for interactive applications. A program cannot (easily) feed back into another. Limited support for concurrency (as each program needs all data before it starts). Need to get all data through the system before we can see results. 141
Peer-to-peer (P2P) architectural style
143 Peer-to-peer A peer-to-peer (P2P) is any distributed network architecture composed of participants that make a portion of their resources (such as processing power, disk storage or network bandwidth) directly available to other network participants, without the need for central coordination instances (such as servers or stable hosts).
144 Peer-to-peer /cont. P2P systems are like client-server but all processes can be both clients and servers simultaneously. Peers are both suppliers and consumers of resources (in contrast to the traditional client-server model where only servers supply, and clients consume).
145 Peer-to-peer /cont. They are more flexible but also more complicated than client-servers: potential problems include deadlock , or starvation . Absence of centralization makes resource discovery an important issue for P2P applications.
Peer-to-peer /cont. A deadlock is a situation wherein two or more competing actions are each waiting for the other to finish, and thus neither ever does. Starvation is a situation where a process is continuously denied access to necessary resources, thus never being able to complete its task. 146
147 Peer-to-peer /cont. In a pure P2P application, queries for information are issued to the network of peers; requests propagate until the information is discovered or some propagation threshold is passed. If and once the desired information is located, the peer obtains the direct address of that peer and contacts it directly. This style is limited by the discovery algorithm and the network bandwidth available. Hybrid applications optimize this process by having certain peers play special roles, either for locating other peers or for providing directories locating information.
Event-based architectural style
149 Event-based, implicit invocation: Key characteristics An event can be defined as “a significant change in state.” Instead of sending a message to a receiver object, a component can announce (or broadcast) one or more events .

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture