魅力基于Web的教学资源共享平台的用户系统设计-英文文献及翻译

2021年1月24日发(作者：美国街头篮球)
基于
Web
的教学资源共享平台的用户系统设计
-
英文文献及
翻译

英文参考文献原文及译文


英文参考文献原文复印件及译文

专

业
:
计算机科学与技术

姓

名
:
张洪源

学

号
: 110210121
指导教师
:
孙胜娟

完成日期
2015
年
6
月

英文参考文献原文及译文

英文原文

Database Model Introduction
Gilmore
A database (sometimes spelled data base) is also called an
electronic database, referring to any collection of data or information,
and that is specially organized for rapid search and retrieval by a
computer. Databases are structured to facilitate the storage, retrieval,
modification, and deletion of data in conjunction with various data-
processing operations .Databases can be stored on magnetic disk or tape,
optical disk, or some other secondary storage device.
A database consists of a file or a set of files. The information in
these files may be broken down into records, each of which consists of
one or more fields. Fields are the basic units of data storage, and each
field typically contains information pertaining to one aspect or
attribute of the entity described by the database. Using keywords and
various sorting commands, users can rapidly search, rearrange, group,
and select the fields in many records to retrieve or create reports on
particular aggregate of data.
Complex data relationships and linkages may be found in all but the
simplest databases. The system software package that handles the
difficult tasks associated with creating, accessing, and maintaining
database records is called a database management system(DBMS). The
programs in a DBMS package establish an interface between the database
itself and the users of the database. (These users may be applications
programmers, managers and others with information needs, and various OS
programs)
A DBMS can organize, process, and present selected data elements
form the database. This capability enables decision makers to search,
probe, and query database contents in order to extract answers to
nonrecurring and unplanned questions that aren’t available in regular
reports. These questions might initially be vague and/or poorly defined,
but people can “browse” thr
ough the database until they have the
needed information. In short, the DBMS will “manage” the stored
data items and assemble the needed items from the common database in
response to the queries of those who aren’t programmers.

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英文参考文献原文及译文

A database management system (DBMS) is composed of three major parts:
(1) a storage subsystem that stores and retrieves data in files; (2) a
modeling and manipulation subsystem that provides the means with which
to organize the data and to add, delete, maintain, and update the data;
(3) and an interface between the DBMS and its users. Several major
trends are emerging that enhance the value and usefulness of database
management systems:
1. Managers: who require more up-to-data information to make
effective decision.
2. Customers: who demand increasingly sophisticated information
services and more current information about the status of their orders,
invoices, and accounts.
3. Users: who find that they can develop custom applications with
database systems in a fraction of the time it takes to use traditional
programming languages.
4. Organizations: that discover information has a strategic value;
they utilize their database systems to gain an edge over their
competitors.
The Database Model
A data model describes a way to structure and manipulate the data in
a database. The structural part of the model specifies how data should
be represented (such as tree, tables, and so on). The manipulative part
of the model specifies the operation with which to add, delete, display,
maintain, print, search, select, sort and update the data.
Hierarchical Model
The first database management systems used a hierarchical model-that
is-they arranged records into a tree structure. Some records are root
records and all others have unique parent records. The structure of the
tree is designed to reflect the order in which the data will be used
that is, the record at the root of a tree will be accessed first, then
records one level below the root, and so on.
The hierarchical model was developed because hierarchical
relationships are commonly found in business applications. As you have
known, an organization char often describes a hierarchical relationship:
top management is at the highest level, middle management at lower
levels, and operational employees at the lowest levels. Note that within
a strict hierarchy, each level of management may have many employees or
levels of employees beneath it, but each employee has only one manager.
Hierarchical data are characterized by this one-to-many relationship
among data.
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英文参考文献原文及译文

In the hierarchical approach, each relationship must be explicitly
defined when the database is created. Each record in a hierarchical
database can contain only one key field and only one relationship is
allowed between any two fields. This can create a problem because data
do not always conform to such a strict hierarchy.
Relational Model
A major breakthrough in database research occurred in 1970 when E. F.
Codd proposed a fundamentally different approach to database management
called relational model, which uses a table as its data structure.
The relational database is the most widely used database structure.
Data is organized into related tables. Each table is made up of rows
called and columns called fields. Each record contains fields of data
about some specific item. For example, in a table containing information
on employees, a record would contain fields of data such as a person’s
last name, first name, and street address.
Structured query language (SQL) is a query language for manipulating
data in a relational database. It is nonprocedural or declarative, in
which the user need only specify an English-like description that
specifies the operation and the described record or combination of
records. A query optimizer translates the description into a procedure
to perform the database manipulation.
Network Model
The network model creates relationships among data through a linked-
list structure in which subordinate records can be linked to more than
one parent record. This approach combines records with links, which are
called pointers. The pointers are addresses that indicate the location
of a record. With the network approach, a subordinate record can be
linked to a key record and at the same time itself be a key record
linked to other sets of subordinate records. The network mode
historically has had a performance advantage over other database models.
Today, such performance characteristics are only important in high-
volume, high-speed transaction processing such as automatic teller
machine networks or airline reservation system.
Both hierarchical and network databases are application specific. If
a new application is developed, maintaining the consistency of databases
in different applications can be very difficult. For example, suppose a
new pension application is developed. The data are the same, but a new
database must be created.
Object Model
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英文参考文献原文及译文

The newest approach to database management uses an object model, in
which records are represented by entities called objects that can both
store data and provide methods or procedures to perform specific tasks.
The query language used for the object model is the same object-
oriented programming language used to develop the database application.
This can create problems because there is no simple, uniform query
language such as SQL. The object model is relatively new, and only a few
examples of object-oriented database exist. It has attracted attention
because developers who choose an object- oriented programming language
want a database based on an object-oriented model.
Distributed Database
Similarly, a distributed database is one in which different parts of
the database reside on physically separated computers. One goal of
distributed databases is the access of information without regard to
where the data might be stored. Keeping in mind that once the users and
their data being separated, the communication and networking concepts
come into play.
Distributed databases require software that resides partially in the
larger computer. This software bridges the gap between personal and
large computers and resolves the problems of incompatible data formats.
Ideally, it would make the mainframe databases appear to be large
libraries of information, with most of the processing accomplished on
the personal computer.
A drawback to some distributed systems is that they are often based
on what is called a mainframe-entire model, in which the larger host
computer is seen as the master and the terminal or personal computer is
seen as a slave. There are some advantages to this approach. With
databases under centralized control, many of the problems of data
integrity that we mentioned earlier are solved. But today’s personal
computers, departmental computers, and distributed processing require
computers and their applications to communicate with each other on a