Semantic Relationships

To achieve these consistencies, MODEL.LA. provides a series of semantic relationships among its modeling elements, which are defined at different levels of abstraction. For example, the semantic relationship (see 21 1), is-disaggregated-in, triggers the generation of a series of relationships between the abstract entity (e.g., overall plant) and the entities (e.g., process sections) that it was decomposed to. The relationships establish the requisite consistency in the (1) topological structure and (2) the state (variables, terms, constraints) of the systems. For more detailed discussion on how MODEL.LA. maintains consistency among the various hierarchical descriptions of a plant, the reader should consult 21 1. 

Catalysis models have clear semantic relationships to one another. At any level of abstraction, they form an important part of the inspection criteria for those models. Across levels of refinement, these rules, together with the rules for refinement, provide a concrete basis for design reviews. 

If the modeling elements of LCR represent the modes of a network, the semantic relationships constitute the links (edges) of the network. There... 

The first two semantic relationships establish the structure of a modeling element they allow the declaration of the attributes and methods of a modeling element. Although all object-oriented systems possess, by definition, the first two semantic relationships and no special computer-aided provisions are needed, they have been included here for completeness. 

The following two semantic relationships establish the links between a basic modeling element and its derivative subclasses of modeling objects and instances. Both of them are isomorphic mappings. 

Specification mappings, described by the following sbc semantic relationships, are used to specify the value of attributes of various modeling elements. They express, (a) binary relations, such as whole/ part links, (b) communication lines among modeling objects, or (c) the value of simple describing properties. 

The is-attached-to semantic relationship establishes linkages between different modeling elements, allowing flow of information from one to the otherfs). Furthermore, since atoms know their membership into various functional groups, auxiliary links are automatically established thus LCR creates automatically the following semantic connection ... 

The addition of descriptive attributes and methods to each of these new modeling classes further characterizes each class. To characterize the modeling class excited-state-effects, we add attributes and methods descriptive of singled (S) and triplet (T) states. The states are refined further by energy level. For example ground states (S(,To) are differentiated from their excited states (S,T,) as well as from their higher states (S2,T2, and S3,T3). As before, we link these attributes using the semantic relationship is-attribute-of ... 

The semantic relationship is-characterized-as is used for this purpose. It provides a window for viewing the more interesting behaviors/ structures associated with a class, such as... 

We initiate the development of covalent-bond by creating the modeling element and establishing the normal superclass links using the semantic relationship, is-a (Fig. 9) ... 

We can also specialize these methods according to physical requirements and chemical requirements. This provides an abstraction barrier between what is true (i.e., the physical laws) and what is believed to be true (i.e., current theory). For example, suppose that the methods favor-able-interatomic-distance-p and potentially-stable-bond-formation-p are physical requirements whereas the methods available-bonding-electron-p and proper-orbital-symmetry-p are chemical requirements. We represent this to covalent-bond by associating the top-level methods (i.e., methods associated with K j ), chemical requirements, and physical requirements, to covalent-bond directly (i.e., we override the method inherited by the mother model class). This is accomplished using the semantic relationship is-method-of, as was demonstrated earlier ... 

We then tailor these methods by associating the methods of covalent-bond to them. This is achieved using the semantic relationship is-composed-of ... 

We also establish a second (redundant) link using the semantic relationship is-described-by. In addition, LCR establishes automatically the follow-... 

Figure 11a presents several of the pathways identified when s-BuOH is formed during the initiation process. The attributes of the initiation reaction, initiation-1, for the oxidation of butane are presented in Fig. 12a, where objects are denoted by . Note that each of these objects can in turn be expanded or disaggregated using the semantic relationships. Figure 12b illustrates one of the many pathways, pathway-1, generated during the oxidation of butane into s-BuOH and AcEt. The expansion of the object, (initiation-l), an element in the value of the attribute, composing-reactions, results in the description shown in Fig. 12a. The user has access to this information at every step of the synthetic process using the semantic relationships provided by LCR (see Section III.E).

To demonstrate the utility of LCR and the interaction between various modeling elements, semantic relationships, and supporting methods, let us first consider the pyrolysis of ethane forming principally ethylene and hydrogen. Although this example is relatively simple, it highlights the functionality of LCR and underscores various issues that require resolution for computer implementation to be successful. 

MODEL.LA. possesses the same set of 13 semantic relationships as LCR, with the same semantic implications ... 

---