Program schema

THEOREM 4.17 Every partially computable function can be computed using the set of program schemas obtained by applying one WHILE construction to a STEP scheme and using interpretations of function letters limited to S(x), Z(x), ... 

Manna, Zohar, "Program Schemas," in Currents in the Theory of Computing,... 

A similar study is made by [O Keefe 90], who uses algebraic specifications. The predicates of such specifications can be directly plugged into given logic program schemas. Several schemas may be applicable according to the properties (associativity, commutativity, existence of left identities, and so on) of the identified predicates. 

These recurrence relations are then plugged by the so-called Basic Synthesis Theorem into a LISP program schema that reflects a divide-and-conquer design strategy. This yields the following LISP program ... 

Algorithm (and program) schemas are an old, and ever popular, idea of computer science. They have been proposed for a huge variety of applications. 

Each object has the ability to serialize itself and also to initialize itself from a serialized representation. If the programming language has a reflective facility, you can write a single piece of code to determine the structure of the object and perform serialization and initialization. Java serialization works this way. Of course, flat files do not provide any of the multi-user, concurrency, meta-data, schema evolution, transaction, and recovery facilities that a database provides. 

Remember that you are modeling the business, and not writing a database schema or program or modeling purely physical relationships. The associations are attributes drawn in pictures and not lines of communication or physical connections. (The latter would normally be drawn as an action.)... 

Let me give you some hints on how I write simple programs for generating computer poetry. The several sets of three-line computer poems that follow were all generated by the random selection of words and phrases that are placed in a specific format, or semantic schema. My... 

Database schemas are centrally stored and controlled. Data definitions (schema) are stored in the centralized data dictionary. The user s view(s) of the database is defined and stored in the same data dictionary. Programs are given access to individual data fields, records, sets and areas of the database on a need-to-know basis. The database administrator creates and maintains integrity of the database schemas. The benefits of this approach are ... 

C. The database may be modified without affecting the application programs. Only those programs affected by the schema changes need to be recompiled. 

Chapter 5 shows how schema theory can be practically implemented. It gives a detailed description of one example of schema-based instruction, the Story Problem Solver (SPS). SPS is a computer-based system of instruction constructed around schema theory, using the basis set of schemas developed in chapter 3. It provides fundamental instruction enabling students to build schemas. A second computer program, the Problem Solving Environment (PSE), is also described in chapter 5. PSE provides an exploratory environment in which students can practice and utilize their schema knowledge about story problems. 

The Story Problem Solver (SPS) is a computer-implemented program of instruction about arithmetic story problems.1 My research group and I developed SPS as an explicit instructional test of schema theory.2 Its companion, the Problem Solving Environment (PSE), is also a computer-based system, one that provides no additional instruction but that serves instead as a practice arena in which we can evaluate students acquisition of schema knowledge. Both SPS and PSE are written in Lisp and run on Xerox 1186 computer workstations equipped with 19-inch display monitors and three-button optical mice. In this chapter, I first describe SPS and its instructional objectives and then explain the contributions of PSE. 

An example of how novel items can fail to address key schemas may be informative. This example derives from the California Assessment Program (CAP), which for several years was a national leader in the movement to develop open-ended questions for mathematics assessment. As part of the CAP Mathematics Advisory Committee, I worked with the rest of the committee in reviewing items which had been field-tested to determine their suitability, including those that were used in the first statewide... 

Schema evolution is the ability to change deployed schemas, i.e., metadata structures formally describing complex artifacts such as databases, messages, application programs, or workflows. Typical schemas thus include relational database schemas, conceptual ER or UML models, ontologies, XML schemas, software interfaces, and workflow specifications. Obviously, the need for schema evolution occurs very often in order to deal with new or changed requirements, to correct deficiencies in the current schemas, to cope with new insights in a domain, or to migrate to a new platform.

K2 [13] is a distributed query system that has been developed at the University of Pennsylvania. K2 relies on a set of data drivers, each of which handles the low-level details of communicating with a single class of underlying data sources (e.g., Sybase relational databases, Perl/shell scripts, the BLAST family of similarity search programs, etc.). A data driver accepts queries expressed in the query language of its underlying data source. It transmits each such query to the source for evaluation and then converts the query result into K2 s internal complex value representation. Data drivers are also responsible for providing K2 with data source metadata (i.e., types and schemas), which are used to type check queries. 

For routine database maintenance such as backup, each RDBMS provider typically supplies other command line programs. For example, PostgreSQL provides the pg dump program that outputs a file of SQL commands containing the definition and data contained in each table, schema, etc., in the database. This file becomes a backup of the database, which can be restored using the psql command to execute the SQL commands in the file. 

The view itself is not stored as a copy of the subset of the table. Rather, the view is a dynamic representation of the subset that changes as rows of the corresponding tables are updated, inserted, or deleted. A view is analogous to a program or a function that is executed when necessary to provide a result. It is stored in a schema in the database and can be used anywhere in an SQL statement that a table can be used. However, it is not possible to insert rows into or to update rows of a view. Instead, the original table or tables containing the data must be updated. 

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. 

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