Execution Model. It is convenient to conceptually assume that two versions of a program are run in parallel when considering the semantics of a change contract between two versions of a program. Recall that a change contract concerns currently only sequential programs as JML does, and the introduced parallelism is not intended to interfere with Java’s multithreading. The overall semantic rule shown in Figure 5(b) clarifies such a parallel execution model. Given two commands c1 and c2 that represent the method bodies of the previous and updated versions, respectively, we assume they are run in parallel as denoted with c1 c2. \ \ \ || Nonetheless, not all parallel executions c1 c2 are interesting to the users of a change contract. For example, given a change contract, ensures result== prev( result)+1, of a method m(int x), one would expect the increase of the return value only when the same integer value for parameter x is given to both versions. Roughly speaking, input equality between the two versions needs to be assumed when considering a change contract. However, naive input equality is not enough for two reasons. First, the prior parameter x may not be of a primitive type but of a subtype of Object. If this is the case, simple reference comparison is inappropriate. Second, there may be structural changes such as addition of a method parameter or a field. To address the first issue, we compare object graphs instead of object references. Conventionally, two graphs are considered isomorphic if there is a unique one-to-one correspondence between the vertexes and edges of the two graphs. If, in addition, all the one-to-one corresponding vertexes that represent primitive values of the two object graphs contain the same values, the two object graphs are considered isomorphic. We extend this notion of isomorphism to the program state level as follows. Note that a program state consists of a store σ and a heap h. ≈ Definition 1 (Isomorphic Program States). Two program states (σ1, h1) and (σ2, h2) are considered isomorphic to each other if, for all variables x that commonly exist in the domain of σ1 and σ2, the two object graphs that σ1(x) and σ2(x) respectively refer to are isomorphic to each other. We denote the fact that two program states (σ1, h1) and (σ2, h2) are isomorphic to each other with notation (σ1, h1) (σ2, h2). As usual in Java programs (and other object-oriented programs), the receiver of an object (i.e., this) is considered an implicit parameter of a nonstatic met...
Execution Model. ATG World Markets Ltd offers OTC trading via an automatic validation Dealing Desk execution model. ATG World Markets Ltd will act as a dealer and is the counterparty to any trades that you undertake. In this model, ATG World Markets Ltd compensation may not be limited to our standard markup and our interests may be in direct conflict with yours. Each transaction you open constitutes a contract with us; these contracts can be closed only with us and are not transferable to any other person. This also means that you may be exposed to the risk of our default.
Execution Model. ATG World Markets Ltd offers OTC trading via an automatic validation Dealing Desk execution model. ATG World Markets Ltd will act as a dealer and is the counterparty to any trades that you undertake. In this model, ATG World Markets Ltd compensation may not be limited to our standard markup and our interests may be in direct conflict with yours. Each transaction you open constitutes a contract with us; these contracts can be closed only with us and are not transferable to any other person. This also means that you may be exposed to the risk of our default. For more information, please download our Risk Disclaimer Policy 执行模型 ATG World Markets Ltd 通过自动验证交易平台执行模型提供 OTC 交易。 ATG World Markets Ltd 将充当经销商，并且是您从事的任何交易的交易对手。在这种模式下，ATG World Markets Ltd 的赔偿可能不仅限于我们的标准加价，我们的利益可能与您的利益直接冲突。您开立的每笔交易均构成与我们的合同；这些合同只能与我们完成，不能转让给任何其他人。这也意味着您可能会面临我们违约的风险。 有关更多信息，请下载我们的风险免责声明政策
