数据库系统基础教程Database-Systems-2.pptx

The Relational Model of Data ;Database: what? consist of ? DBMS、DBA、DBS Transaction properties : ACID Atomicity; Consistency;Isolation; Durability; Relational data model、DDL 、Concurrency control、Logging and recovery、Indexes、 Client/Server MySQL、SqlServer 、Oracle ; An Overview of Data Models Basics of the Relational Model Defining a Relation Schema in SQL An Algebraic Query Language Constraints on Relations ;A data model is a notation(符号) for describing data or information. Conceptual model(概念模型) Database data model: the description generally consists of three parts: Structure of the data relational model = tables; network and hierarchical models = graphs/trees. Operations on the data Constraints(约束) on the data;Important Data Models: The Relational Model, including object-relational extensions; The Semistructured-data Model, including XML(扩展标记语言) and related standards; Network and Hierarchical data Models High-Level Database Model The Entity/Relationship Model Object Definition Language;title;Why Relations? Provides a simple, limited approach to structuring data. Provides a limited, yet useful, collection of operations on data. They allow us to implement languages, such as SQL, that enable the programmer to express their wishes at a very high level. ;Attribute(属性): The columns of a relation are named by attributes. Each attribute of a relation has a name, describes the meaning of entries in the column below. Any two attributes of a relation can’t have same name.;Relation schema = relation name and the set of attributes. Example: Movies (title, year, length, genre) or Movies (title:string, year:integer, length:integer, genre:string) We can reorder the attributes of a relation, without changing the relation. Example: Movies (year, title, length, genre);Relational database = collection of relations. Relational database schema = set of all relation schemas in the database.;title;How to describe a tuple? Use commas to separate components, and use pa