Operators, Boolean

The initial step is to identify which database, from a few thousands worldwide (about 10 000 in 2002), provides the requested information. The next step is to determine which subsection of the topic is of interest, and to identify typical search terms or keywords (synonyms, homonyms, different languages, or abbreviations) (Table 5-1). During the search in a database, this strategy is then executed (money is charged for spending time on some chemical databases). The resulting hits may be further refined by combining keywords or database fields, respectively, with Boolean operators (Table 5-2). The final results should be saved in electronic or printed form. 

Databo e-s and Data Sources in Chemi-stry 231 Table 5-2. Basic search tools of Boolean operators and truncation. 

Answers from aH of these searches contain CAS Registry Numbers. Answer sets may be combined, using the Boolean operators AND, OR, or NOT, with other answer sets or with text terms, such as names or molecular formulas. Any answer set also may be used to define subsets of the file for subsequent stmcture searching. Answer sets of up to 10,000 Registry Numbers from any type of search in this file may also be used as search terms in other files, such as the CA or CAOLD files (53). 

A set G of logic gates is universal if an arbitrary ri-variable Boolean function T can be written as a composition of the logic gates in G a universal set of gates 9u- - dm is. sometimes also said to gorm a basis set for T. It is easy to show that the set consisting of the Boolean operators AND, OR and NOT, for example, is universal. ... 

Consider an arbitrary set of Boolean input values, Xi,..., Xn- Using only the Boolean operators AND and NOT, we can write down an expre.ssion which takes the value 1 if and only if a particular configuration of O s and I s appears in the input. Suppose that n = 6 and we want to construct an expression that equals one if and only if xi = X3 = X4 = X5 = 1 and. X2 = xe = 0. A little thought will show that the required expression is given by joining the string of six Boolean variables with the AND operator, substituting NOT(xi) for all values x)i that are required to equal zero ... 

Fig. 6.6 TVuth tables for the universal Boolean operators NAND and NOR.

The words AND, NOT, and OR are called Boolean operators. They may be combined in many ways, for example,... 

An invariant is a Boolean expression. The usual Boolean operators (as used in programming languages) are available there are different ways of writing them depending on your preferences. Tables 2.1, 2.2, and 2.3 display them. 

The primitive types that we use in every model and design—Boolean, arithmetic, sets, lists, and dictionaries—can be defined in basic packages that are imported by all others. These types are most easily defined in an axiomatic style—that is, by simply stating a number of fundamental facts (axioms, mathematicians call them) that are true about the types, from which other facts follow. For example, the package defining Boolean operators contains the propositions shown in Figure 9.46. 

The various chemical requirements of each derivative group are summarized in Table 8.1. In order to implement these requirements, a component specification language has been developed. This specification language contains a combination of keywords, target values, and Boolean operators. A brief summary of these commands is listed in Table 8.2 below. The specification language allows the user to control... 

The result of any retrieval command in MAECIS is a set of chemical structures which is referred to as the "current set". If a second retrieval is made, the current set is moved into another internal storage area and is referred to as the "prior set". In this way, MAECIS automatically keeps track of at least two retrievals for the user. However, it is often necessary to establish several sets of molecules during a single computer session. In MAECIS, any number of sets can be retained using a SAVE command which allows the user to name and save any set of molecules created by a retrieval command. Any stored set in MAECIS can also be referenced in a subsequent FIND command. Thus, new sets can be generated from old sets through the find command s boolean operations. Sets retained with the SAVE command are in temporary memory. To make them permanent, the STORE and RESTORE commands are available to move sets to and from permanent disk files. 

The second step performs the GRID calculation with a given probe on the three subunit models. In order to make the application of Boolean operations with the map files as easy as possible, the matrix dimension of the GRID box is exactly maintained as in the largest model, i.e. that with a+fi subunits, maintaining, for both subunits, the original complex atom coordinates. The three maps obtained are named A, B and C, respectively (Fig. 7.1). 

The ETIC file has been divided into three different portions by the MEDLARS system. The ETIC citations from 1981 to the current date are found on TOXLINE. References dated 1976 to 1980 appear in a separate file entitled T0XBACK76, while those citations through 1975 and previous years are found in T0XBACK65. Search strategy on these three files is identical. Terms may be entered singly or may be combined by means of the Boolean operators AND, OR, and AND NOT. 

If a keyword consists of a phrase which contains a word identical to a Boolean operator, this word must be changed (e.g., AID can be substituted for AND). This is important to remember when using the terms describing biological end points as listed in Table 3. A search for craniofacial defects resulting from dichlorvos exposure can be worded ETIC AND 62-73-7 AND CRANIUM AID FACE (KW). 

The CAD design generated the geometry by performing Boolean operations on simple volumic primitives [2], The microstructure was realized by microstereolithography. This technique is based on a layer-by-layer light-induced polymerization of a liquid resin, a pre-polymerized solution. Actually, about 1800 layers of 5 pm thickness were superimposed in this way (5 h manufacturing time). 

PubMed is one of the most valuable web resources for biochemical literatures accessible from Entrez (http //www.ncbi.nlm.nih.gov/entrez/). Many well-regarded journals in biochemistry, molecular biology and related fields as well as clinical publications of interest to medical professionals are indexed in PubMed. The resource can be searched by a keyword with its boolean operators (AND, OR and NOT). Users can specify the database field to search. The Preview/Index menu allows the user to build a detailed query interactively. 

At the same time, the remaining adder may be using the sum produced by the first adder on a previous machine cycle and the result from a shift boolean operation to perform a subtraction. The ultimate goal, of course, is to get as many functional units... 

As you search your electronic sources, remember that you may have to try a variety of keywords (and their synonyms) to find what you need. Sometimes your keyword search may turn up too few leads—and sometimes you may be overwhelmed with too many matches (For example, when Amy Lawrence typed in the keyword Anastasia, she discovered too many irrelevant entries focusing on Hollywood movies about the princess.) To save time and effort, you may be able to broaden or narrow your search by typing in words called Boolean operators as illustrated below ... 

Not all databases respond to Boolean operators, however, so it s always best to consult the searching advice offered by your particular information system. 

Most search engines have their own searching tips to improve your chances for a successful search, it s well worth the time to read the advice. For example, many search engines allow use of some or all of the Boolean operators (see page 375) to narrow or broaden your search. Some allow the use of plus and minus signs to show connected terms or unwanted matches ... 

Step 5 The initial conditions are obtained by dehning the following two functions. The function/nl takes the value 1.0 for x > 0.25 and the function/n2 takes the value 1.0 for X > 0.75. Thus, the initial condition is satisfied by the expression fnl —fn2. In FEMLAB, this is achieved using the Boolean operator... 

Databases can be searched by simple Boolean operations using both structural keys and fingerprints. The latter have a higher information density than structural keys without losing specificity. Hence, database searches using fingerprints instead of structural keys are more efficient. 

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