DATABASE SYSTEMS THOMAS CONNOLLY & CAROLYN BEGG PDF

Discuss the main differences between these data models. Compared with the relational model, relationships are explicitly modeled by the sets, which become pointers in the implementation. Again, data is represented as collections of records and relationships are represented by sets. However, the hierarchical model allows a node to have only one parent. A hierarchical model can be represented as a tree graph, with records appearing as nodes also called segments and sets as edges. See Section 2.

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Discuss the main differences between these data models. Compared with the relational model, relationships are explicitly modeled by the sets, which become pointers in the implementation. Again, data is represented as collections of records and relationships are represented by sets. However, the hierarchical model allows a node to have only one parent. A hierarchical model can be represented as a tree graph, with records appearing as nodes also called segments and sets as edges. See Section 2.

Give an example of a transaction. A transaction is a series of actions, carried out by a single user or application program, which accesses or changes the contents of the database.

A mechanism to ensure that the database is updated correctly when multiple users are updating the database concurrently. This avoids inconsistencies from arising when two or more transactions are executing and at least one is updating the database. How does database integrity differ from database security? Although integrity is related to security, it has wider implications: integrity is concerned with the quality of data itself.

Integrity is usually expressed in terms of constraints, which are consistency rules that the database is not permitted to violate.

Exercises 2. What type of language does each system provide? What type of architecture does each DBMS use? Check the accessibility and extensibility of the system catalog. Is it possible to export the system catalog to another system? To do this you will need to obtain appropriate information about each system. There should be manuals available or possibly someone in charge of each system who could supply the necessary information. Write another program that stores names and addresses in a database.

Modify the programs to use external, conceptual, and internal schemas. What are the advantages and disadvantages of this modification? The programs can be written in any suitable language and should be well structured and appropriately commented. Two distinct files result. The structures can be combined into one containing name, address, and telNo, which can be the representation of both the internal and conceptual schemas.

The conceptual schema should be created separately with a routine to map the conceptual to the internal schema. The two external schemas also must be created separately with routines to map the data between the external and the conceptual schema. The two programs should then use the appropriate external schema and routines. Extend the program so that it stores the format of the data in the database; in other words, create a system catalog.

Provide an interface that makes this system catalog accessible to external users. Again, the program can be written in any suitable language. It should then be modified to add the data format to the original file. This should not be difficult, if the original program is well structured. The interface for other users operates on the data dictionary and is separate from the original program.

A menu-based interface is adequate.

EL UNDECIMO MANDAMIENTO NO MATARAS TUS SUEOS PDF

Thomas Connolly Carolyn Begg Thomas Connolly Carolyn Begg

Database Design Methodology that can be Used by Both Technical and Non-technical Readers Database design methodologyis explicitly divided into three phases based on the widely accepted Entity—Relationship model: conceptual, logical, and physical. Each phase is described in a separate chapter with an integrated case study of the methodology working in practice. To help the reader use the methodology and understand the important issues, the methodology has been described using a realistic worked example, based on an integrated case study, DreamHome. Three additional case studies are provided in Appendix B to allow readers to try out the methodology for themselves. The methodology in each phase is presented as a series of steps. For the inexperienced designer, it is expected that the steps will be followed in the order described, and guidelines are provided throughout to help with this process.

DIN 4102-2 PDF

L. Alan Winters

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