小區物業管理系統(論文)開題報告和英文翻譯t(編輯修改稿)

　

【文章內容簡介】 gative point concerns absence of data protection features． Unless encrypted, data cane accessed by whoever has access to the machine Data can be destroyed through mistakes or maliciousintent. The second weakness of manv of the PCbasedsystems is that of performance. If data volumes growup to a few thousands of records， performance couldbe a bottleneck． For anization where growth in data volumesis expected, availability of, the same or patiblesoftware on large machines should be considered. This is one of the most mon misconceptionsabout database management systems that are used inpersonal puters． Thoroughly prehensive andsophisticated business systems can be developed indBASh, Paradox and other DBMSs． However, theyare created by experienced programmers using theDBMS39。s own programming language. That is not thesame as users who create and manage personal filesthat are not part of the mainstream pany system． Data security prevents unauthorized users from viewing or updating the database． Using passwords, the database, called subschema(pronounced subscheme)， For example, an employee database can contain all the data about an individual employee, but one group of users may be authorized to view only payroll data, while others are allowed access to only work history and medical data. The DBMS can maintain the integrity of the database by not allowing more than one user to update the same record at the same time, The DBMS can keep duplicate records out of the database, for example, no two customers with the same customer numbers (Key fields) can be entered into the DataBase. When a DBMS is used, the detailed knowledge of the physical anization of the data does not have to be built into every application program. The application program asks the DBMS for data by field pine, for example, I coded representation of give customer name and balance due would be sent to he DBMS． Without a DBMS, the programmer must secrecy space for the full structure of the in the program, Any change in data structure requires￡ hangs in all the applications programs． The multipledatabase model is represented by proposals for shared and private database architect rues, checkout and checking of data to and from shared and private databases． Each user may populates/her private database with data checked out of the shared database, perform updates against the data. and check them back into the shared Database. The multipledatabase model can be used to work around the conflict situations inherent in long lunation database sessions． Since each user from the shared database and work against. is/her private database, disconnected from the、 hared database (at least on the surface)， the usersan avoid the conflict situations． In particular, multile users may be simultaneously updating the same thought having to wait for other users to ate late their updates． However, when updated is to benecked into the shared database, it may have to be checked in as a new version, necessitating version management. Further, 39。when data in a private database references data in the shared data， or vice versa, a private database is not really disconnected from the shared database. For example, the evaluation of query in general will require the database system to access both a private database and the shared database, even if the query may have been formulated against a private database． The multipledatabase model is more appropriate than the singledatabase model in an environment where it is easy to determine in advance logical partitions of the database that correspond to work to be performed. The singledatabase model has received considerably more attention than the multiple database model． The focus of research into singledatabase model has bee