Database systems concepts 4th edition phần 5

Hãy để chúng tôi xem xét làm thế nào chúng tôi xử lý các truy vấn trên một cây + B. Giả sử rằng chúng ta muốn tìm thấy tất cả hồ sơ với giá trị tìm kiếm chính của V. Hình 12,10 trình bày giả để làm như vậy. Bằng trực giác, thủ tục hoạt động như sau. Đầu tiên, chúng tôi kiểm tra các nút gốc, tìm kiếm các giá trị tìm kiếm chính nhỏ nhất lớn hơn V. | Silberschatz-Korth-Sudarshan Database System Concepts Fourth Edition III. Object-Based Databases and XML 10. XML The McGraw-Hill Companies 2001 Background 363 bank account account-number A-101 account-number branch-name Downtown branch-name balance 500 balance account account account-number A-102 account-number branch-name Perryridge branch-name balance 400 balance account account account-number A-201 account-number branch-name Brighton branch-name balance 900 balance account customer customer-name Johnson customer-name customer-street Alma customer-street customer-city Palo Alto customer-city customer customer customer-name Hayes customer-name customer-street Main customer-street customer-city Harrison customer-city customer depositor account-number A-101 account-number customer-name Johnson customer-name depositor depositor account-number A-201 account-number customer-name Johnson customer-name depositor depositor account-number A-102 account-number customer-name Hayes customer-name depositor bank Figure XML representation of bank information. Silberschatz-Korth-Sudarshan Database System Concepts Fourth Edition III. Object-Based Databases and XML 10. XML The McGraw-Hill Companies 2001 364 Chapter 10 XML Structure of XML Data The fundamental construct in an XML document is the element. An element is simply a pair of matching start- and end-tags and all the text that appears between them. XML documents must have a single root element that encompasses all other elements in the document. In the example in Figure the bank element forms the root element. Further elements in an XML document must nest properly. For instance account . balance . balance . account is properly nested whereas account . balance . account . balance is not properly nested. While proper nesting is an intuitive property we may define it more formally. Text is said to appear in the context of an element if it appears between the start-tag and end-tag of that element. Tags are .