A database management system (DBMS) is an important type of programming system, used
today on the biggest and the smallest computers. [1]As for other major forms of system software,
such as compilers and operating systems, a well-understood set of principles for database
management systems has developed over the years, and these concepts are useful both for
understanding how to use these systems effectively and for designing and implementing DBMS's.
DBMS is a collection of programs that enables you to store, modify, and extract information
from a database. There are many different types of DBMS's, ranging from small systems that run
on personal computers to huge systems that run on mainframes. The following are the location of
database between application programs and end-users.
There are two qualities that distinguish database management systems from other sorts of
programming systems.
1) The ability to manage persistent data, and
2) The ability to access large amounts of data efficiently.
Point 1) merely states that there is a database which exists permanently; the contents of this
database is the data that a DBMS accesses and manages.
Point 2) distinguishes a DBMS from a
file system, which also manages persistent data. A DBMS's capabilities are needed most when
the amount of data is very large, because for small amounts of data, simple access techniques,
such as linear scans of the data, are usually adequate.
[2]While we regard the above two properties of a DBMS as fundamental, there are a number
of other capabilities that are almost universally found in commercial DBMS's. These are:
Support for at least one data model, or mathematical abstraction through which the user can
view the data.
Support for certain high-level languages that allow the user to define the structure of data,
access data, and manipulate data.
Transaction management, the capability to provide correct, concurrent access to the database
by many users at once.
Access control, the ability to limit access to data by unauthorized users, and the ability to
check the validity of data.
Resiliency, the ability to recover from system failures without losing data.
Data Models Each DBMS provides at least one abstract model of data that allows the user
to see information not as raw bits, but in more understandable terms. In fact, it is usually possible
to see data at several levels of abstraction. At a relatively low level, a DBMS commonly allows
us to visualize data as composed of files.
Efficient File Access The ability to store a file is not remarkable: the file system associated
with any operating system does that. The capability of a DBMS is seen when we access the data of
a file. For example, suppose we wish to find the manager of employee "Clark Kent". If the
company has thousands of employees, It is very expensive to search the entire file to find the one
with NAME="Clark Kent". A DBMS helps us to set up "index files," or "indices," that allow us to
access the record for "Clark Kent" in essentially one stroke no matter how large the file is. Likewise,
insertion of new records or deletion of old ones can be accomplished in time that is small and
essentially constant, independent of the file’s length. Another thing a DBMS helps us do is navigate
among files, that is, to combine values in two or more files to obtain the information we want.
Query Languages To make access to files easier, a DBMS provides a query language, or
data manipulation language, to express operations on files. Query languages differ in the level of
detail they require of the user, with systems based on the relational data model generally
requiring less detail than languages based on other models.
Transaction Management
Another important capability of a DBMS is the ability to
manage simultaneously large numbers of transactions, which are procedures operating on the
database. Some databases are so large that they can only be useful if they are operated upon
simultaneously by many computers: often these computers are dispersed around the country or
the world. The database systems used by banks, accessed almost instantaneously by hundreds or
thousands of automated teller machines (ATM), as well as by an equal or greater number of
employees in the bank branches, is typical of this sort of database. An airline reservation system
is another good example.
Sometimes, two accesses do not interfere with each other. For example, any number of
transactions can be reading your bank balance at the same time, without any inconsistency. [3]But
if you are in the bank depositing your salary check at the exact instant your spouse is extracting
money from an automatic teller, the result of the two transactions occurring simultaneously and
without coordination is unpredictable. Thus, transactions that modify a data item must “lock out”
other transactions trying to read or write that item at the same time. A DBMS must therefore
provide some form of concurrency control to prevent uncoordinated access to the same data item
by more than one transaction.
Even more complex problems occur when the database is distributed over many different
computer systems, perhaps with duplication of data to allow both faster local access and to
protect against the destruction of data if one computer crashes.
Security of Data A DBMS must not only protect against loss of data when crashes occur,
as we just mentioned, but it must prevent unauthorized access. For example, only users with a
certain clearance should have access to the salary field of an employee file, and the DBMS must
be able associate with the various users their privileges to see files, fields within files, or other
subsets of the data in the database. Thus a DBMS must maintain a table telling for each user
known to it, what access privileges the user has for each object. For example, one user may be
allowed to read a file, but not to insert or delete data; another may not be allowed to see the file at
all, while a third may be allowed to read or modify the file at will.
DBMS Types
Designers developed three different types of database structures: hierarchical, network, and
relational. Hierarchical and network were first developed but relational has become dominant.
While the relational design is dominant, the older databases have not been dropped. Companies
that installed a hierarchical system such as IMS in the 1970s will be using and maintaining these
databases for years to come even though new development is being done on relational systems.
These older systems are often referred to as legacy systems.
1, teller ['telə]
n. (美)出纳员;讲述者;讲故事者;计票员
2, reservation [,rezə'veiʃən]
n. 预约,预订;保留
3, at will
随意;任意
Continue reading it-e-32 Introduction to DBMS
2007开始/段落 第三个按钮
一图抵千言

注意红框框里面的内容(1 标题 这样的),不要选别的,选别的就不好排版了。这样之后只要在想要作为标题的行点击样式里面对应的标题级别,word会依据级别来整理。
要自定义的话,可参见
http://blog.sina.com.cn/s/blog_6238dcdb0100qz8j.html
不过比较复杂哦!
Continue reading word 标题自动编号
- 一个业务用例描述的是业务过程——而不是软件系统过程。
- 一个业务用例为涉众创造价值。这些涉众要么是业务参与者要么是业务工作者。
- 一个业务用例可以超越组织的边界。有些构架师对于这一点有非常严密的态度。许多业务用例确实超越来组织的边界,但是有些业务用例仅仅关注于一个组织。
- 1.业务用例就是要完成的业务,系统用例是系统要做的事情,两者的域不同。
- 2.业务建模主要描述了该项目涉及的所有业务,需求模型主要是描述为了满足业务需求系统要做什么,因此,需求模型与业务模型相比,它描述的只是业务模型的一个子集。
- 3.比方说我们设计一个自动提款机系统,它可以满足用户的取款、改密、查询等需求,那么这些需求就是业务用例;但是用户又分为借记卡用户和信用卡用户,那么根据业务规则,不同的卡用户的取款、改密、查询的过程是不一样的,所以系统为了满足这种业务需求会包含到两个子用例里实现,这种子用例就是系统用例。也就是说系统用例就是系统为了满足这种业务需求要做什么。
为什么要区别这些?可能在你的用例图中就混杂了这两种用例。
参见:
http://www.uml.org.cn/requirementproject/200707024.asp
http://gaojiewyh.iteye.com/blog/408363
http://www.cnblogs.com/rhcad/archive/2010/06/11/1756173.html
Continue reading 业务用例与系统用例的区别
Steganography is a method of embedding electronic messages into a media file (for example, an image or audio file) by altering nonessential lines of code; the changes are imperceptible. The message remains undetected until unencrypted. Honeytokens is any kind of tantalizing false data, including phony patient records at a hospital, lists of invalid social security numbersor even simply a word processing file named "HR-salaries," that's stored in a restricted part of the network. If anyone tries to access the files the security team is alerted to the trespassing before the intruder can do any real damage.
1, imperceptible [,impə'septəbl]
a. 不能感知的,不知不觉的,微细的
2, steganography [,stegə'nɔgrəfi]
n. 速记式加密
3, tantalizing ['tæntəlaiziŋ]
a. 诱人的
4, phony ['fəuni]
a. 假的,伪造的
5, trespassing
n. 擅自进入
v. 侵入;犯罪(trespass的ing形式)
6, intruder [in'tru:də]
n. 侵入者,干扰者,妨碍者
Continue reading it-e-31 Steganography and Honeytokens
配置使用的ServiceMix版本是servicemix-3.3,在tomcat5.5以上运行。(因为依赖包大部分是需要jdk1.5)
ServiceMix有三种部署方式:单独程序方式,servlet方式,与Geronimo and JBoss.整合方式。这里主要介绍servlet方式,因为这样可以整合到任何servlet容器中。
Servlet部署需要在web.xml中配置spring加载文件,这种spring是和xbean整合的自定义配置文件。
配置文件说明:
Web.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
<display-name>ServiceMix Web Application</display-name>
<description>Deploys ServiceMix inside a Web Application</description>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/jmx.xml /WEB-INF/core.xml /WEB-INF/activemq.xml</param-value>
</context-param>
Spring配置文件
<context-param>
<param-name>contextClass</param-name>
<param-value>org.apache.xbean.spring.context.XmlWebApplicationContext</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
Spring 监听器
<!-- servlet mappings -->
<!-- the main JMX servlet -->
<servlet>
<servlet-name>JMXServlet</servlet-name>
<servlet-class>org.apache.servicemix.web.jmx.JMXServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<!-- the HTTP binding servlet -->
<!-- START SNIPPET: servicemix-http-->
<servlet>
<servlet-name>HttpManagedServlet</servlet-name>
<servlet-class>
org.apache.servicemix.http.HttpManagedServlet
</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
http bean组件(BC)servlet
<servlet-mapping>
<servlet-name>HttpManagedServlet</servlet-name>
<url-pattern>/jbi/*</url-pattern>
</servlet-mapping>
<!-- END SNIPPET: httpBinding -->
<servlet-mapping>
<servlet-name>JMXServlet</servlet-name>
<url-pattern>/jmx/*</url-pattern>
</servlet-mapping>
</web-app>
demo主要功能的配置在core.xml中:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:sm="http://servicemix.apache.org/config/1.0"
xmlns:http="http://servicemix.apache.org/http/1.0"
xmlns:my="http://servicemix.apache.org/demo/"
xmlns:foo="http://servicemix.apache.org/demo/">
<!-- the JBI container -->
<sm:container id="jbi"
rootDir="#rootDir"
useMBeanServer="true"
createMBeanServer="false"
MBeanServer="#jmxServer"
installationDirPath="#installDir"
deploymentDirPath="#deployDir"
monitorInstallationDirectory="true"
transactionManager="#transactionManager"
depends-on="broker">
<sm:activationSpecs>
<!-- an example HTTP binding for use by the SpringBindingServlet -->
<!-- START SNIPPET: http -->
<sm:activationSpec componentName="servicemix-http" service="foo:httpBinding" destinationService="foo:echo">
<sm:component>
<http:component>
<http:configuration managed="true" />
<http:endpoints>
<http:endpoint service="foo:httpBinding"
endpoint="endpoint"
targetService="foo:echo"
role="consumer"
locationURI="http://localhost/exampleUri/
配置url, 会被tomcat自动转换为serverapp/jbi/ exampleUri
"
defaultMep="http://www.w3.org/2004/08/wsdl/in-out
消息请求方式是in-out,即期望又返回消息
" />
</http:endpoints>
</http:component>
</sm:component>
</sm:activationSpec>
使用http BC,作为一个消费者(consumer)目标指向服务引擎(SE)foo:echo
<!-- END SNIPPET: http -->
<!-- a simple Echo service to test InOut message exchanges using HTTP-->
<sm:activationSpec componentName="echo" service="foo:echo" >
<sm:component>
<bean class="org.apache.servicemix.components.HelloWorldComponent">
<property name="property" value="name"/>
</bean>
</sm:component>
</sm:activationSpec>
SE foo:echo,这是一个简单的helloworld
</beans>
经过这样的配置和在web.xml中配置的servlet,那么uri pattern形如 /jbi/exampleUri会请求foo:httpBinding (BC),在ESB内部foo:httpBinding通过消息路由(normalized message router)与foo:echo通信。
Web测试页面链接为http://localhost:(tomcat端口)/ESB-ServerMix-Web/examples/
需要在firefox下测试。
测试页面使用ajax请求/jbi/exampleUri经过foo:httpBinding, foo:echo处理返回信息。
Continue reading ServiceMix环境配置