To database system pdf

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Nodes are interconnected by means of coordination rules. A coordination rule allows a node i to fetch data from its neighbour nodes j1 ,. Note that we are making the simplifying assumption that the equal constants mentioned in the various nodes refer to equal objects, i. Other approaches consider domain relations to map objects between different nodes [Serafini et al.

A P2P system is just the collection of nodes interconnected by possibly cyclic rules. A user accesses the information hold by a P2P system by formulating a query at a specific node.

Definition 4 Query A local query is a first order formula in the language of one of the local databases DB i. The semantics of a P2P system and of queries is derived from the general logical framework presented in [Franconi et al. Under these assumptions, computing query answers is reducible to data fetching [Franconi et al. To describe the P2P networks we introduce the notion of a dependency edge between nodes of a P2P network. Definition 5 There is a dependency edge from a node i to node j, if there is a coordination rule with head at node i and body at node j.

Note that the direction of a dependency edges is the opposite to that of the rules. The direction of a rule is the direction in which data is transfered, whereas the dependency edge has the opposite orientation. In this paper we use MDB to denote a P2P system, using terms such as P2P system or a network ; please note that we consider the general case when the network is cyclic. I is used to denote a set of all nodes in given MDB, C denotes the set of all coordination rules, and L the set dependency edges between nodes in a network derived from C.

Subsets of I are denoted by A. We assume that I, L, and C are always finite sets. Definition 6 A dependency path for a node i is a path hi1 , i2 ,.

Definition 7 A maximal dependency path for a node i is a dependency path such that if we add any node to the path, the result will not be a dependency path. In this paper, when we describe dependency paths for a node i, we omit the first node i.

Assume that the network MDB consist initially of a set of nodes I, and that C is an initial set of coordination rules with L being the initial set of dependency edges. We define an atomic network change operation as follows. A finite change of a network is a finite sequence of atomic changes. An initial subchange U1 of a change U is a initial prefix of U 4. Definition 9 1. A sound answer of a query Q in a network subject to runtime changes, is an answer to the query that is included in the result that we would obtain if we executed all the addLink statements before running Q, and did not execute the deleteLink statements at all.

A complete answer of a query Q in a network subject to runtime changes, is an answer to the query that contains the result that we would obtain if we executed all the deleteLink statements before running Q, and did not execute the addLink statements at all.

The basic idea behind this definition is that we cannot know in advance what the state of the database will be at termination time. The result with respect to the part that is changed will depend on the order and timing of the execution of the changes. The following theorem states that our update algorithm behaves well with respect to change. Theorem 1 1. For a finite runtime change of a network, the update algorithm will terminate, and it gives sound and complete answers to queries in the network subject to runtime changes.

In the case of an infinite runtime change to the network, the update algorithm may not terminate. However, in general we cannot assume that a network change is finite. In the general case, therefore, the nodes in the network may never reach the fix-point — or at least, we may not be able to show that they have reached a fix-point. We now give a condition on when a subset of nodes can reach a fix-point, even under infinite change of the whole network.

Definition 10 1. A set of nodes A1 is separated from a set of nodes A2 in a P2P network I if there is no dependency path from any node in A1 that involves a node in A2. A set of nodes A1 is separated from a set of nodes A2 in P2P network I with respect to a change U if for any subchange of U there is no dependency path from a node in A1 involving a node in A2 in the network we obtain by applying that subchange.

Lemma 3 For a finite runtime change of the network, the complexity of the update algorithm at each node is in 2EXPTIME with respect to the size of the change. First level architecture rather sophisticated P2P functionalities. As basic functionalities we can distin- guish: definition of a peer on a network; creation of communication links be- tween peers called pipes ; creation of messages, which can envelope arbitrary data e.

Examples of more sophisticated functionalities provided by JXTA are: creation of peer groups; specification of services and their implementation on peers; advertis- ing of network resources i.

It provides IP independent naming space to address peers and other resources, it is independent of system platforms e. We have chosen JXTA since it already gives practically all basic building blocks for developing P2P applications and thus allow the developer to concentrate on implementation of specific functionalities a given application is required to provide.

The first level logical architecture of a node, inspired by [Bernstein et al. Nodes connect to a P2P database network by means of connecting to other peer s , as it is schematically shown on Figure 1 see the arrow from JXTA Layer to the network and arrows between nodes in the network. By means of the UI users can commence network queries and updates, browse streaming results, start topology discovery procedures, and so on.

For instance, user can modify the set of coordination rules w. PDF database. See System Requirements. Description PDF database takes the metadata info and file details from your PDF files and stores it all in a PDF database which you see in a clear table and which you can query with simple, standard database queries. People also like. EasyOCR Free. Folder Synchronizer Free. Additional information Published by Godidog. Published by Godidog.