基于B/S的防伪电子商城系统英文文献
phone number. This definition now needs to be expanded to reflect a new reality. Databases today are used to store objects such as documents, photographic images, sound, and even video segments, in addition to conventional textual and numeric data. For example, the salesperson’s database might include a photo image of the customer contact. It might also include a sound recording or video clip of the most recent conversation with the customer. To reflect this reality, we use the following broadened definition: Data consist of facts, text, graphics, images, sound, and video segments that have meaning in the users’ environment.
We have defined a database as an organized collection of related data. By organize we mean that the data are structured so as to be easily stored, manipulated, and retrieved by users. By related we mean that the data describe a domain of interest to a group of users and that the users can use the data to answer questions concerning that domain. For example a database for an automobile repair shop contains data identifying customers (the data items it lists include each customer’s name, address, work phone number, home phone number, and preferred credit card number), automobiles belonging to those customers (the data items include make, model, and year), and repair histories for each of those automobiles (e.g., date of service, name of person who worked on vehicle, type of repair performed, and dollar amount of work performed).
Databases range from a single user with a desktop computer to those on mainframe computers with thousands of users. The range of database applications can be divided into four categories, from simplest to most complex: personal computer (or PC) databases, workgroup databases, department databases, and enterprise databases. We introduce each category with a typical example, followed by some issues that generally arise within the category of use.
1. Personal Computer Databases
Personal computer (PC) databases are designed to support one user with a standalone personal computer (for example, a desktop or laptop computer). For example, consider a company that has a number of salesperson who call on actual or prospective customers. Each salesperson might carry a laptop computer with a simple database application to record customer information and the details of contacts with each customer.
Personal computer databases are widely used because they can often improve personal productivity. However, they entail a risk: the data cannot easily be shared with other users. For example, suppose the sales manager wants a consolidated view of customer contacts. This cannot be quickly or easily provided from an individual salesperson’s databases. This illustrates a very common problem: if data are of interest to one person, they probably are (or will soon become) of interest to other as well. For this reason, personal computer databases should be limited to those rather special situations (such as in a very small organization) where the need to share the data among users of the personal computer database is unlikely to arise.
2. Workgroup Databases
A workgroup is a relatively small team of people who collaborate on the same project or application or on a group of similar projects or applications. A workgroup typically comprises fewer than 25 persons. These persons might be engaged (for example) with a construction project or with developing a new computer application. A workgroup database is designed to support the collaborative efforts of such a team.
Consider a workgroup that develops both standard and custom objects (or software components) that are sold to software vendors as well as to end users. Typically one or more persons work on a given object or component at a given time. The group needs a database that will track each item as it is developed and allow the data to be easily shared by the team members.
3. Enterprise Databases
An enterprise database is one whose scope is the entire organization or enterprise (or, at least, many different departments). Such databases are intended to support organization-wide operations and decision making. Note that an organization may have several enterprise databases, so such a database is not inclusive of all organizational data. A single, operational, enterprise database is impractical for many medium to large organizations due to difficulties in performance for very large databases, diverse needs of different users, and the complexity of achieving a single definition of data (metadata) for all database users. An enterprise database does, however, support information needs from many departments. Arguably the most important type of enterprise database today is called a data warehouse.
Consider a large health care organization that operates a group of medical centers including hospitals, clinics, and nursing homes. each of these medical centers has a separate (or databases) to support the various operations at that facility. These databases contain data concerning patients, physicians, medical services, business operations, and other related entities.
The databases provide adequate support for most functions at each individual medical center. However, the organization has increasing has increasingly realized the need for a single, consolidated view of the entire organization; for example, to see the total activities with a single patient of reasons: corporate decision making, dealing with external suppliers (such as insurance companies), and reporting to various agencies. To satisfy these requirements, the organization has created a data warehouse that is maintained at the corporate office. Data in the data warehouse are derived by extracting and summarizing data from the individual databases on a periodic basis and transmitting those data by means of a telecommunications network to the corporate data warehouse.
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