Ns2 project in christchurch

         Ns2 project in Christchurch this synchronization is strictly not necessary; in general, redactions may occur as soon as a metarule is mat,ched. Thus, base rule ns2 project in Christchurch and metarule evaluations may be pipelined. This observation motivaks the development of the centralized two-phase Match/Tag-Fire scheme in the rest of this section. The basic ns2 project in Christchurch algorithm can be extended to the distributed case as well. We outline various distributed schemes t8hat may utilize t,he basic two-phase ns2 project in Christchurch pipeline processing method in the next, section.

In the basic centralized version ns2 project in christchurch of tthe algorithm, all sites send their rule instance as they are generated to the MRP. The goal is to have the metarule processing at the MRP nearly ns2 project in Christchurch completed by the time the last instance is received from the slowest site. This is called “two-phase rnetarule processing” , outlined in and is discussed below. There ns2 project in Christchurch is one IR for each rule in the rule program. The relation scheme for an IR is obtained by conjoining the schema of the relations referenced on the LHS of the rule. As instances of base rules are received by the MRP, they are stored in the appropriate IR. For each ns2 project in Christchurch instance received at the MRP, a structure is created to represent the set of all metarules that are capable of redacting that instance.

This is called a “Wait-For”  structure, and can be viewed as a tree. The instance in question is at the root, and each child node represents ns2 project in Christchurch the LHS conditions of,a relevant metarule, represented as a list of conditional expressions that appear in the metarule. Since this is a metarule, a conditional expression is applied to instance relations as opposed to base relations.

Ns2 project in Auckland

      Ns2 project in Auckland we need not recompile and reconfigure the object level system, only the metarule system. Third, as discussed in , it may be required in order for incremental update through metarules to be performed correctly. The operational ns2 project in Auckland semantics of PARULEL suggests a natural decomposition of overall processing into three separate phases, namely, match, redact, and fire. 

      Our proposed implmentation seeks to ns2 project in Auckland remove the separation between object-level rule matching , which produces rule instances, and the subsequent filtering of these instances using the metarules , into a ns2 project in Auckland single “pipelined” process. Thus, the obvious three-phase Match-Redact-Fire cycle is replaced by a of a set of metarules, is to be evaluated against a database D. Each of multiple distributed sites has its own copy of the entire database D, and its own copy of ns2 project in Auckland  the entire production rule program, where some or all of the rules have ns2 project in Auckland been modified to be constrained on certain attributes .

     Thus, site i has, such that  where B is the operator that applies a set of rules against the database D. A naive, centralized approach to handling the matching of metarules against a database of production ns2 project in Auckland rule instances is as  All sites match base rules, and send resulting ns2 project in Auckland  instances to a queue read by a single, centralized nietarule processing (MRP) site. MRP gathers all instances from all sites.MRP matches all instances against ns2 project in auckland the set ofMRP reports back to appropriate sites which inmet arules. stances are firable. Clearly, under ns2 project in Auckland the naive approach, the MRP cannot proceed until all instances have been received from all base rule matching sites.

Ns2 project in Sydney

       Ns2 project in Sydney this idea is rather simple and al-lows for an easy metarule implementation by using the object level rule ns2 project in Sydney matc,her verbatim. However, this is probably inefficient since it forces the object level system to execute various phases of metarule evaluation and ns2 project in Sydney object level evaluation alternately through the rule evaluator. Essentially the rule evaluator is used to simulate the metarules. We should seek more efficient implementations than this approach suggests. Rather ns2 project in Sydney  than trying to compile metarules away in terms of the object level system, metarules might be processed as a separate body of code and data structures.

       This is the approach we adopt in PARADISER, and we describe this approach as a “twophase” metarule processing ns2 project in Sydney algorithm in the next two sections. We provide both centralized and distributed ns2 project in sydney versions of this method in some detail. Here the idea is that the object level system carries out its normal operation producing instances that are sent to the metarule matcher as messages. Data structures similar to those used in the network matchers are used to ns2 project in Sydney evaluate metarules.

      It is dearly an eager approach, and is designed especially for distributed evaluation cases. Why might this be a better approach than folding metarules into the object level system directly as outlined above since it incurs expensive instance communication overhead First, there may be no choice if one is using a distributed computing ns2 project in Sydney environment. Communication is a necessity and thus separating the metarule implementation from the object level implementation is more than sensible. Second, one ns2 project in sydney may wish to run a different set of metarules against the same object level rules.

Ns2 project in perth

       Ns2 project in perth the semantics of metarules dictates that when there are two or more conflicting rule instances, some particm lar ns2 project in perth instance should be redacted. Can we define a total ordering over rule instances and use lazy matching ns2 project in perth at the network nodes applied to instances so that only the single rule instanc,e that would be fired is generated and those that would be redacted would not even be generated? The answer is no. Preference here is not dependent upon lexicographic sort of ns2 project in perth a totally ordered WM as in OPS5.

     Preference here meansprogrammer supplied preference based upon arbitrary conditions on bound values in instances that are dynamically ns2 project in perth computed and that, may not define a total ordering. It is unlikely that lazy match will be effective in systems with set-oriented semantics as described here. Our goal is to compute and execute as many instances, and thus as many working memory transactions, in ns2 project in perth a single inference cycle as possible.

     We do not seek to compute a single firable rule as quickly as possible in a single inferenc,e c,yc.le by reducing the ns2 project in perth amount of irrelevant match work as in lazy evaluation. Rather, we attempt ns2 project in perth to make all match work as relevant as possible by eliminating conflicting rule instances according to a set of user specified metarules. Another possible metarule implementation discussed in  is as follows. We compile the rnetarules into object level rules while rewriting the object level rules mentioned in the metarules. Here, the object level rules are changed so ns2 project in perth that they always fire but assert an “instance’ object in the object level WM. Metarules match against these instance objects, and when a metarule fires, its actions are not redactions, but the RHS actions of the rules that they would have allowed to fire.

Ns2 project in melbourne

      Ns2 project in Melbourne the first technique consists of compiling metarules into the object level matcher. This means that if one ns2 project in melbourne is using a RETE  or TREAT discrimination net matcher, for example, one can compile the metarule tests into the network. At the network nodes where final instance tokens are ns2 project in melbourne generated, one can insert additional test nodes, compiled from the metarules, and ns2 project in melbourne thus inhibit certain instances from proceeding onward to the firing mechanism, i.e., redact them.

      This is practical when considering main memory based systems. Instances can simply ns2 project in melbourne be treated like any othertoken in this case If aggregate metarules are supported, however, we have several problems. First, the network nodes storing instance tokens will likely grow very large especially when computing aggregate ns2 project in melbourne metarules. The performance of memory based systems would degrade significantly.

     Second, an ‘Laggregate condition” to be tested at these nodes will have to be inhibited until all ns2 project in melbourne  instances have been computed. Thus, some means of determining when the match is completed and all instances have been computed is needed. This approach is ns2 project in melbourne essentially the same as the one proposed in . Now let’s consider base metarules for a moment in this context. The approach is very straight.forward. How might it be more intelligent Lazy tnatching works for OPS5 because it is possible to define a ns2 project in melbourne total ordering over WM elements. Match runs faster since it stops searching for instances once one is found. The computed instance is guaranteed to be the same instance chosen ns2 project in melbourne from an eager computation. In metarule matching, one can presumably stop as soon as one instanc. e is found too. But this is not the case.

Ns2 project in brisbane

       Ns2 project in Brisbane but one cannot determine apriori what a metarule programmer might actually specify . Object level rule ns2 project in Brisbane matching may be lazy, as in nLEAPS, or eager as in PARULEL and SOAR. In the case of lazy evaluation, one would expect the matcher to produce the instances that would be ns2 project in Brisbane fired after metarule redactions without generating the instances that would be redacted.

     However, this is im-practical, since for an instance to be redacted, it must be matched and ns2 project in brisbane bound in the LHS of a metarule and participate in conditional expressions between other rule instances. Indeed, a single instance may participate in many different ns2 project in Brisbane metarules and thus may be matched against a number of instances generated by different object-level rules. This implies that the “redactable instances” must be generated and ns2 project in Brisbane tested in the LHS of the metarule along with other rule instances.

    Thus, lazy evaluation is not an appropriate evaluation strategy since it seeks to generate only one instance at a time. Furthermore, for languages with set-oriented semantics, lazy ns2 project in Brisbane evaluation would necessarily require repeated invocation to generate a stream of instances to saturation before proceeding to fire those instances, lazy evaluation would be a ns2 project in Brisbane step in the most inner loop of an eager evaluation computation. Thus, it is difficult to see how lazy matching can be folded into the object level match phase, or ns2 project in Brisbane whether it is desirable at all. The metarule matching method that one adopts is influenced by the considerations cited above. In the rest of this paper, we ns2 project in Brisbane attempt to enumerate specific feasible techniques and briefly outline their characteristics.

Ns2 project in adelaide

       Ns2 project in Adelaidein the initial definition of PARULEL, we allow conditional expressions in the LHS of ns2 project in Adelaide metarules. These conditions evaluate arithmetic expressions containing values bound in the ns2 project in adelaide object level rule instances. In certain cases one may want a more expressive ns2 project in adelaide metarule that computes some arbitrary “aggregate” condition on its LHS that is ns2 project in Adelaide applied to a set of matching base rule instances. For example, one may choose to fire a set of rule instances  if the number of those instances is greater than the number ns2 project in adelaide of instances generated by another distinct object level rule. We distinguish these two cases as “base” metarules and “aggregate” metarules. Each poses different problems ns2 project in Adelaide for metarule matching.

      The initial PARADISER implementation uses a replicated database configuration where multiple processing sites are involved in rule evaluation. Each processing site has a distinct constrained version of the rule program. Metarule matching is complicated by the fact that instances at one site may need to be nmcommunicated to ns2 project in Adelaide another site in order for a metarule to be matched fully.

    If we choose not to communicate instances and do all metalevel processing at each individual site, additional burden is ns2 project in Adelaide placed on the compile time distribution and reorganization subsystem, which is also responsible for load balancing of base rule evaluations the case of aggregate metarules, the point is moot; all instances might have to be comrnunicated to one site that computes ns2 project in Adelaide the aggregate function against the set of instances. Of course, it may be possible to compute the aggregate function in parallel among the sites if the function ns2 project in adelaide in question is associative mand commutative.

Ns2 project in Finland

      Ns2 project in Finland besides the issue of parallelism, RPL provides a declarative framework for conflict resolution like that proposed for PARULEL. However, it appears that the attributes of the firing groups used for conflict ns2 project in Finland resolution are hard-coded; there is no actual way of accessing the conflict set itself. Another system related to PARlJLEL is RDL. Although the execution semantics is defined as nondeterministic. choice for rule execution, control can be specified separately from the ns2 project in Finland rules by way of a control language based upon regular expressions.

       In early work , one of the authors defined a rule language controlled by a separate control language based upon regular expressions, that specified sequential, repetitive , alternative, and permutable  ns2 project in Finland rule executions. Although useful, the approach had a major problem in practice. Occasionally the control expression being followed required the execution of a ns2 project in Finland rule that had no instantiations. Ultimately, metarules were defined to resolve these “control conflicts”, which then quickly subsumed the entire regular expression language, metarules provided sufficient specification of c,ontrol.

     As we have noted, there is of ns2 project in Finland course the problem with strict specification of control sequences by way of rule names. It is impossible to specify control on the basis of data matched by rules, nor can ns2 project in Finland one specify control between instances of the same rule. PARULE’L’s metarules ameliorate these problems. PARULEL programs consist of a set of object-level rules which are matched against base relations  and a set of metarules that specify control ns2 project in Finland of rule execution by way of inhibiting the firing of rule instances. There are several issues related to the overall rule system that is relevant to efficient ns2 project in Finland matching of metarules, which we describe below.

Ns2 project in Yukon Territory

      Ns2 project in Yukon Territory the metarules of PARlJLEL enable the specification of either kind of control. However, they are best suited for expressing heuristic preferexes for the purpose of filtering a conflict set of rule instances ns2 project in Yukon Territory and obtaining a subset for concurrent firing. PARULEL has similarities with some existing rule languages, although the flexibility of the system in terms of the ability to customize the ns2 project in Yukon Territory conflict resolution method and the operational semantics in a “programmable” fashion for a particular application is unique. Consider RPL , a rule language with programmable conflict resolution expressed by metarules. Although there are obvious syntactic differences between RPL and PARULEL , there are also fundamental differences between the two.

       RPL appears to provide only tjwo mechanisms to express parallelism. The “all” ns2 project in Yukon Territory construct dictates that all instances of a rule should be fired. But this is useful only if all instances of a single rule can be fired at once without conflict, ns2 project in Yukon Territory otherwise one has t,o resort to “fire-one-instance” semantics.

   In contrast, PARIJLEL’s metarules provide the means of redacting unwanted instances of the same rule as well as different rules, and firing all that remain in parallel. The “firing group” construct of RPL is its second major construct that, is reminiscent of various rule ns2 project in Yukon Territory partitioning schemes in other earlier work . Here the idea of representing “commutative” rules by way of mutually exclusive rule clusters is provided. But nofurther optimizations are applied, and hence no large gain in parallelism can be expected PARULEL’s execution is intended to be optimized by way of copy-and-constraining  of rules ns2 project in Yukon Territory distributed to different processing sites. Optimizations may also be applied according to rule interdependence analysis as described in.

Ns2 project in Nova Scotia

       Ns2 project in Nova Scotia this section is a brief description of PARULE, a rule language with parallel execution semantics. ns2 project in Nova Scotia PARULEL syntax is derived from OPS5, while mits operational sernantic.s resemble those of Datalog’. PARULEL programs consist of “object-level” prodnction rules, “metarules” for a ns2 project in Nova Scotia programmable operational semantics, and a database of facts. Object-level rules consist of a conjunctive left–handside of conditions which are tested against the database of facts and a right hand side  of actions to be performed on the database. The LHS ns2 project in Nova Scotia corresponds to rule bodies of Datalog-style languages, and the RHS corresponds to rule heads. The object-level rules encode the basic, problem solving knowledge.

       The “programmable” conflict resolution strategy is realized via meta-level rules, ns2 project in Nova Scotia that express domaindependent relationships among the rule instantiations in ns2 project in Nova Scotia the conflict set at any given cycle. These metarules specify what specific types of interactions among rule instances indicate a conflict. The action of these metarules is to remove, or redact, one or more of the conflicting rule instances from the conflict set.

      The post-redaction conflict set is considered to be conflict-free, and can be fired concurrently, The ns2 project in Nova Scotia ease and flexibility with which control can be specified for problem solving has long been a useful metric for the richness of a programming language, and has ns2 project in Nova Scotia influenced language design considerably. In the PARULELlanguage, metarules express control. Control may involve the scheduling of sequential tasks, or expressing ns2 project in Nova Scotia preferences among competing parallel paths.