Lecture 29 11/4/15. CMPSC431W: Database Management Systems. Instructor: Yu- San Lin

Transcription

1 CMPSC431W: Database Management Systems Lecture 29 11/4/15 Instructor: Yu- San Lin Course Website: hcp:// Slides based on McGraw- Hill & Dr. Wang- Chien Lee 1

2 DTD Examples <!ELEMENT BOOKLIST (BOOK)*> Element BOOKLIST consists of zero or more BOOK elements <!ELEMENT BOOKLIST (BOOK)+> Element BOOKLIST consists of one or more BOOK elements <!ELEMENT BOOK (AUTHOR, TITE, PUBLISHED?)> A BOOK element contains a AUTHOR element, a TITLE element, and an op[onal PUBLISHED element. 2

3 Regular Expression exp1, exp2, exp3: A list of regular expressions exp*: an op[onal expression (zero or more occurrences) exp?: an op[onal expression (zero or one occurrence) exp+: a mandatory expression (one or more) exp1 exp2: exp1 or exp2 3

4 DTD Examples (cont.) <!ELEMENT LASTNAME (#PCDATA)> LASTNAME is an element that does not contain other elements, but contains actual text Content types Element content: elements that only contain other elements Mixed content: elements also contain #PCDATA 4

5 DTD Examples (cont.) <!DOCTYPE BOOKLIST [ <!ELEMENT BOOKLIST (BOOK)*> <!ELEMENT BOOK (AUTHOR, TITLE, PUBLISHED?)> ]> <!ELEMENT AUTHOR (FIRSTNAME, LASTNAME)> <!ELEMENT FIRSTNAME (#PCDATA)> <!ELEMENT LASTNAME (#PCDATA)> <!ELEMENT TITLE (#PCDATA)> <!ELEMENT PUBLISHED (#PCDATA)> <!ATTLIST BOOK GENRE (Science Fiction) #REQUIRED> <!ATTLIST BOOK FORMAT (Paperback Hardcover) "Paperback"> 5

6 JSON Schema Although JSON is one of the most popular formats for exchanging data on the web, its valida[on rule is not yet fully developed JSON Schema is a standard (currently in drab) which provides coherent schema by which to validate a JSON item against 6

7 { "type": "object", "properties": { } "book": { "type": "object", }, "properties":{ } "genre": { }, "format": { } "author": { }, "title": { }, "type": "obejct", "properties": { "firstname": { "type": "string" }, "lastname": { } "type": "string" }, "required": ["lastname", "firstname"] "type": "string" "published": { } "type": "string", "type": "string" "enum": ["Science", "Fiction"] "type": "string", "enum": ["Paperback", "Hardcover"] JSON Schema: Example 7

8 Scraping Data from the Web One of the most common way of collec[ng data from the web is data scraping Data scraping oben involves ignoring binary data (usually images or mul[media data), display formaeng, redundant labels, etc. Data scraping is oben done when an API of the desired data source is not provided 8

9 Tools for Web Scraping Other sobware Beau[fulSoup 9

10 Data- Intensive Internet Systems Can be divided into three separate func[onal components: Data management Applica[on logic Presenta[on The system architecture determines whether theses three components reside on a single system ([er) or are distributed across several [ers 10

11 Single- Tier Architecture All func[onality combined into a single [er Usually on a mainframe User access through Advantages: Easy maintenance and administra[on Disadvantages: Today users expect graphical user interfaces Centralized computa[on of all of them is too much for a central system 11

12 Client- Server Architectures Applica[on Logic Client Network DBMS Client Client implements only the graphical user interface Server implements business logic and data management 12

13 Client- Server Architectures (cont.) Client implements both the graphical user interface and the business logic Server implements data management Disadvantages: No central place to update the business logic Security issues: server needs to trust clients Does not scale to more than several 100s of clients DBMS Network Client Applica[on Logic Client Applica[on Logic 13

14 Three- Tier Architectures Two- [er architecture separates presenta[on from the rest. Three- [er separates further: Primary interface to the user Need to adapt to different display devices Implements business logic Implements complex ac[ons, maintains states Accesses different data management systems One or more standard database management systems 14

15 Three- Tier Architecture (cont.) Client program (Web browser) JavaScript Cookies Applica[on logic (Applica[on server) Servlets JSP XSLT Data storage (Database system) XML Stored Procedures 15

16 Three- Tier Architecture (cont.) DBMS Applica[on Logic Client DBMS Network Applica[on Logic Network Client DBMS Applica[on Logic 16

17 Presenta[on Tier Provide forms through which users can issue requests, and display responses that the middle [er generates Code should be easy to adapt to different display devices and formats Can be achieved through 17

18 Middle Tier Implements business logic: Controls what data needs to be input Controls flow between mul[- ac[on steps Controls access to the database layer Assembles dynamically generated HTML pages from database query results 18

19 Three- Tier Architecture: Example #1 Airline reserva[ons Database system Airline info, available seats, customer info, etc. Applica[on server Logic to make reserva[ons, cancel reserva[ons, add new airlines, etc. Client program Display forms and human- readable output; field validity checking. 19

20 Three- Tier Architecture: Example #2 Course enrollment Database system Student info, course info, instructor info, course availability, pre- requisites, etc. Applica[on server Logic to add a course, drop a course, create a new course, etc. Client program Display forms and human- readable output; field validity checking. 20

21 Advantages of Three- Tier Architecture Heterogeneous systems Applica[ons u[lize strengths of different plaporms and sobware components at different [ers Thins clients Clients only need enough computa[on power for the Integrated data access Data can be accessed from several sources 21

22 Advantages of Three- Tier Architecture (cont.) Scalability to many clients Each client is lightweight and all access to the system is through the Sobware development benefits Business logic is centralized à easy to maintain Interac[ons between [ers occurs through well- defined, standardized à each applica[on [er can be built out of reusable components 22

23 Don t Forget Next week: Mon (11/9) Review session Homework #4 due Tue (11/10) Midterm 2 part 1, evening Wed (11/11) No class Fri (11/13) Midterm 2 part 2, in class 23

24 References David Walsh, 2010, JSON Valida[on with JSON Schema, hcps://davidwalsh.name/json- valida[on Maximilian Koegel et. al, 2015, The what and why of JSON(Schema), hcp://eclipsesource.com/blogs/2015/06/22/the- what- and- why- of- jsonschema/ 24