db4o Pascal Hauser

Transcription

1 db4o & Object Databases 1

2 Agenda Database vs. Database Management System Types of DBMS s db4o Introduction db4o Querying db4o Features db4o Pros & Cons db4o Applicability Conclusion Discussion 2

3 DB versus DBMS DB = Database Access Layer Structured Storage of Data Additional Data Transaction Log for Data Integrity Indexes (Performance) Bound to Application Client Application DB Access Software Physical Storage File Block Device 3

4 DB versus DBMS DBMS = Database Management System Structured Storage of Data Additional Data Stand-Alone / Self-Running Management Infrastructure DB Access Software Client Application Physical Storage File Block Device 4

5 O(O)/OR/R-DBMS RDBMS = Relational DBMS Data stored in Tables Normalized Referential Integrity Student IDStudent Firstname Lastname StudentModule IDStudentModule FKStudent FKModule Module IDModule ModuleName 5

6 O(O)/OR/R-DBMS ORDBMS = Object Relational DBMS RDBMS with OO- Capabilities Relational Data Model like RDBMS Additional Object Model Mapping between Models SQL Extensions for Object Access Student IDStudent Firstname Lastname StudentModule IDStudentModule FKStudent FKModule Module IDModule ModuleName 6

7 O(O)/OR/R-DBMS O(O)DBMS = Object (Oriented) DBMS Object Model 1:1 Mapping between Application Objects and Data Model Objects 7

8 db4o db4o is an Object Database db4o is a Product db4objects is the Company developing db4o db4o is released as Dual License GNU GPL v2 Commercial License Commercial License comes with Support etc. 8

9 db4o Introduction 1/3 db4o is an Object Database It is NOT a DB management system Available for Java &.NET Simple to use (more follows) Client Application db4o Library Physical Storage File 9

10 db4o Introduction 2/3 Code Examples Save an Object Load an Object 10

11 db4o Introduction 3/3 Code Examples Delete an Object 11

12 db4o Query Examples 0/4 12

13 db4o Query Examples 1/4 Query by Example Query 13

14 db4o Query Examples 2/4 Native Query Delegates Native Query Lambda Expression 14

15 db4o Query Examples 3/4 (a) S.O.D.A Query 15

16 db4o Query Examples 3/4 (b) C# Excurse 16

17 db4o Query Examples 4/4 LINQ Query 17

18 db4o Features 1/7 Rep.A Replication db4o supports replication (through a Component called db4o Replication System (drs)) Again, really simple to use Must be integrated into the Application No stand-alone / administratively managed Replication 18

19 db4o Features 1/7 Rep.B Replication Supports Replication between two db4o Databases Supports Replication to other systems through Hibernate (NOT supported on.net) Two-Way synchronization (Merge) with Conflict Resolution (left to the Developer) Tricky to get it running! NOT a stable component 19

20 db4o Features 1/7 Rep.C Code Sample 20

21 db4o Features 2/7 Evolv.A Evolving Object Structures During Development, Object Model evolves After Release, Data must not be lost How to migrate Data? Code Sample 21

22 db4o Features 3/7 Index.A Indices, for better Performance db4o supports Indices Indices specified in Configuration File Indices can only be specified on a Field Advanced Concepts like Full-Text Search are NOT supported No Index Configuration 22

23 db4o Features 4/7 Conc.A Concurrency Supported, but only as a Workarround Use Semaphores based on Object Identifier db4o Context holds a central shared Semaphore store Results in one Semaphore per Object All Concurrency Problems like locking in the right order are left to the programmer Performance? 23

24 db4o Features 4/7 Conc.B Code Sample 24

25 db4o Features 5/7 Cache.A Caching Needed for loading Objects When loading the same Object twice (per Context), References should point to the very same object This is CONTRARY to working with RDBMS Done anyway for Performance Supports Lazy-Loading Is per Transaction (NOTE: Only ONE Transaction per Context possible) 25

26 db4o Features 6/7 Security No support by db4o Needs to be fully controlled by the Application Access to File can be controlled by Operating System mechanisms Pro: No limitations; everything is possible Con: Even simple Authentication has to be hand made 26

27 db4o Features 7/7 CS.A Client/Server Architecture db4o supports a Client/Server Architecture DB File can be opened for Server use When running as Server, a Network Connection is available, additionally to the full Client possibilities. Only a Network possibility, with additional User/Pass Authentication; NOTHING more! Remember, it is NOT a DBMS! Meaning the Server is tightly coupled with the Client. A.NET Client can NOT access a Java Server! 27

28 db4o Features 7/7 CS.B Caches Per Transaction (as seen before) Multiple Clients => Multiple Transactions Data can get Stale Refresh supported Client Application Client +Hosting Application Cache DB Access Software Cache DB Access Software Physical Storage File Block Device 28

29 db4o Tools 1/1 Commercial Tools ObjectManager(Visual Studio Plug-In) Class View Object View Query Builder Statistics Free Tools Db4oEclipse (Eclipse Plug-In) Reproduction of ObjectManager Developed by the Community (Last Version: 0.2 by 2006) 29

30 db4o Pros & Cons 1/2 Pro Simplicity Small Memory Footprint No Impedance Mismatch when using OO- Languages (Zero Administration) Community Active Development 30

31 db4o Pros & Cons 2/2 Contra Simple System, can (mostly) not replace traditional Systems Many Features not or not completely implemented Heavily Version dependant db4o throws many General Exceptions 31

32 db4o Applicability 1/2 db4o is good for Data Store for a Single-User Application Data Store on Embedded/Mobile Devices Mostly everywhere where you want to store your Objects and not your Data (normally called Object Serialization) 32

33 db4o Applicability 2/2 db4o is NOT good for High Availability Applications Applications where Data is in Foreground Heterogeneous Data Access Storing huge amount of Data 33

34 Conclusion db4o can be a good solution, but it is only appropriate for SPECIFIC scenarios. Prototype to check if it fulfills ALL your needs! 34

35 Discussion 35

36 References Hauser 2008, Review of db4o from db4objects db4objects , Website db4o , Source Code (of Version 7.7) Additional References can be found in the References stated above. 36

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