Client program functions

The RDBMS is installed and runs on a computer that functions as a database server. Any SQL commands are executed on the server by the RDBMS. Functions written in SQL or in any of the procedural languages mentioned above are also executed by the RDBMS. This has the advantage that the data tables used by these SQL commands or procedural functions are under the control of the server. This is the most efficient way to access the data. The disadvantage is that the server may have many requests to handle from many users. Another way to operate on data tables is indirectly, using a client program typically (although not necessarily) run from another computer. 

There is a smaller set of tools that are typically run on the server. Any SQL commands and any procedural language functions are run on the server. In principle, there is complete flexibility of the server side tools, since in principle any computer program can be written in any computer language. Later chapters of this book show how the RDBMS server itself can be extended using server side programming to handle chemical information. These extensions may directly solve the needs of a particular project, but more importantly they increase the flexibility of the RDBMS to handle chemical information. Client programs can use the results of chemical searches and other computations as well. 

The smiles to symbols and smile to bonds functions return arrays of values. In the sample output above, the smiles to bonds output has been truncated for easier viewing. Some client programs may expect this information as separate rows, as if they were records in a file. These arrays may be cast into that form by using a plpgsql function that returns elements of an array as rows. This is shown in the next section. 

A traditional client program reads from a molecular structure file and performs some computation that depends on the molecular structural data. This read(file) function reads particular columns or fields from the file. A different function would be necessary for each type of file format. A traditional client program can be modified to read molecular structure data from... 

The previous section shows how molecular structures stored in an RDBMS can be made available to client programs that traditionally read molecular structure files. The advantage of storing molecular structures in an RDBMS is that the information can be used from within the database, as well as by external clients. For example, it would be possible to search a table of molecular structures for three-dimensional overlap, much like it might be searched for substructure match. Of course, such search functions need to be written and installed as extensions to an RDBMS, just like the matches functions was done for substructure searches. This section shows some possible ways this might be accomplished. 

One disadvantage of using client programs is that data must be transferred to and from the server. Depending on how much data is required, this can cause a client program to run less efficiently than a server function run as an extension of the RDBMS. 

Most new client programs will benefit from a judicious use of both new server-side SQL functions and new client functions. It is wise to carefully consider which operations are best done on the RDBMS server and which are done using a client program. There are several suggestions to consider in designing the best system for a project. 

The marvin sketch SQL function can be called from any client program using database access methods described in Chapter 5. The marvin sketch program can be modified to allow specification of the sketch applet size, loading an initial SMILES, or any other option provided by the Marvin sketch applet. 

This addition does not correct the issues with tautomers, but it does allow an easy way to detect tautomers in the database. Note also that alerting the user is the responsibility of the client program and is not performed in this trigger function or in any of the other constraints in the registration schema. 

If SMILES is used to store molecular structures in a relational database management system(RDBMS), it may be necessary to extract the symbol and bond information for some client programs that expect a connection table. The smiles to symbol and smiles to bonds function shown in the next sections allow the symbol and bond information in a SMILES to be extracted as an array. Some client programs may prefer to process this information in rows, as if they were records in a file. The following plpgsql functions can be used to present the array elements as rows. Two functions are shown ctable (connection table) and symbol coords. The symbol coords function requires an array of coordinates in addition to the symbols. 

The client program invokes a remote procedure function called the client stub. 

Figure 4.3 describes the functionality of the cross-tool situation analyzer of the warehouse. A client tool (here the flowsheet editor) calls the the service offered by the PDW Query Assistant, a Java-based control program. The call contains an identifier for the selected flowsheet element (the separation device) and an operation to be executed on the device (realize). This information is available in the process-integrated flowsheet editor as part of the current situation, intention and the currently running process fragment (cf. Subsect. 3.1.3). This process fragment will also be responsible for handling the information returned by the Query Assistant later on. 

A typical SDK allows using specific functionality of software outside its client in a program code. An SDK may be restricted to just communication or can provide reuse of functionality, like sending out data and receiving some calculated values. 

In addition to these application-functional layers, some functions are needed to support interactions between clients and servers via networks. All the distributed software that supports interaction between application components and network software is called middleware. Middleware is a generic term for all the software components that allow us to connect separate layers or components and put them into a complete distributed system. It provides an application programming interface (API) that isolates application codes from the underlying network communication formats and protocols. It also supplies intermediate system services such as security, naming, directory, messaging, and transaction management services ... 

In each step in tliis multi-level process, the inference rule essentially activates what has previously been built. Tlierefore, if the last build was the appUcation specification, we can offer data (since that is what the application expects), and activate tlie application with tliat data, using the inference rule. Tliis will illustrate the functional behaviour actually captured in the specification, which may or may not be the same as eitlier what tlie specifier intended or wliat the client wanted There is an analogy to testing tlie correctness of a program with data, but here it is tlie correctness of the behaviour defined by tlie specification tliat is being tested by reasoning tliat is, without any code having been written. 

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