Database System (1)

Database:

  • 一組多維的資料集合,其中的記錄會有關聯性,使得使用者可以不同角度取用
  • 資料庫的概念分層

       1.user(使用者) 2.Application software(應用軟體) 3.Database managerment system(資料庫管理系統) 4.Actual database(真實資料庫)

Schemas(真實資料庫):

  • 總覽(Schema):維護資料庫時所需的一個整體資料庫結構的描述:A description of the stucture entire database
  • 個覽(Subschema):對個別使用者需求在資料庫的部份描述[功用:防止較敏感的資料被位授權的人員取得]

Database managerment system資料庫管理系統:

  • Database managerment system(DBMS) :A sofeware layer that manipulates(運用) a database in respond to request from applications(應用).
  • Distributed Database 分散資料庫 : A database stored on multiple machines  [DSMS will mask(偽裝、保護) this organization detail from it users.
  • Data independence 資料獨立 : The ability to change the organization of a database without changing the application sofeware(應用程式) that uses it.

Data model 資料庫模式:

  • A conceptual view(概念觀點) of a database :
    •  
      • Relational database model 關聯性資料庫模式
      • Object-oriented database model 物件導向資料庫模式

Relational database model:

  • Relation(關連表):A rectangular table
  • Attribte(屬性):A column in the table
  • Tipie(列錄):A row in the table
  • Data are organized in two-dimensional tables called relation.
  • The "ROBMS" is the only database models in wide use today.The hierarchical and network models are obsolete(過時的).
  • Each column in a relation is called an attribute.The number of attributes in a relation is its degree.
  • Each row in a relation is called a tuple. The number os row in a relayion is its cardinality.