Presentation on theme: "Object storage and object interoperability"— Presentation transcript:
1 Object storage and object interoperability Access layerObject storage and object interoperability
2 Database management system is a set of programs that enables the creation and maintenance of the related data.The fundamental purpose of DBMS is to provide a reliable, persistent data storage facility and the mechanisms for efficient, convenient data access and retrieval.
3 Difference between DBMS and file system Each application defines and implements the files it requires.Meta data is encapsulated.DBMS:A single repository of data is maintained which can be defined once and accessed by various users.It contains full description of data (schema or metadata) along with data.Format of metadata is independent of any application.
4 Database views Physical view : how data are stored Logical view: what data are stored. It uses logical concepts such as fields, records and tables and their relationships.
5 1. Database modelsIt is the collection of logical constructs used to represent the data structures and data relationships within the database.Two categories:Conceptual models: focuses on logical nature of the data. What is represented in the dataImplementation models: concerned with how it is represented.
6 1.1 hierarchical models It represents data as a single rooted tree. Each node represents a data object and connections represent parent-child relationshipIt represents super-sub relationship of objects.Motor vehicleBusTruckCar
7 1.2 network modelA network model record can have more than one parent.CustomerSoupOrder
8 1.3 relational model Its like tables The columns are attributes that defines the data or value entry for that column.The rows are tuples, represents individual data values.Primary key:Single valueCombination of one or more attributes whose value identifies the entry in the table.Foreign key:Primary key of one table that is embedded in another table to link them.
9 2. Data base interfaces Database schema and data definition language: It is used to specify structure and relationship between the objects.The structure is called database schema.Ex: create schema authorization (Creator)create database database namecreate table tablename (name char (10) not null, dob varchar (10));
10 Data manipulation language and query capabilities: It allows user to manipulate and access the data objects.SQL is the standard DML.
11 3. Object relation mapping 3.1 table-class mapping It is a simple one-to-one mapping of a table to a class.The column of the table is mapped to attributes of class.Single table is mapped to a single class.CostColorMakemodelCarCostColorModelmake
12 3.2 table-multiple classes mapping Single table is mapped to multiple non inheriting classes.Two or more distinct classes have properties that are mapped to columns in a single table.At run time a mapped table row is accessed as an instance of one of the classes based on the column value.
14 3.4 Table-inherited classes mapping A single tables maps to many classes that have common super class.This allows the user to specify the columns to be shared among the related classes.
15 Ex: Name Address Ssn Wage salary Employee Name Ssn address salariedEmployeesalaryhourlyEmployeewage
16 3.5 Tables-inherited classes mapping Translation of is-a relationship.In a relational database is-a relationship is modeled by a primary key that acts as a foreign key to another table.
17 Multi database systems Approach for integrating object oriented application with relational data environment.Heterogeneous information system allow to integrate heterogeneous information sources.Can be structured, semi structured or un structured.Can be constructed over global schema of several databases.So user can access data stored in different databases .This is referred to as federated multi database systems.
18 Multi database systems (MDBS) is a database systems that resides on top of all local database systems and presents a single database illusion to its users.It maintains the global schema which is the integration of all local databases.The schematic differences are handled by neutralization, the process of consolidating local schema.
20 MDBS translates global queries and updates to the appropriate local database for actual processing. Merge the results from the local databases and generate the consolidated result for the user.It coordinates the committing and aborting of global transactions by the local databases.
21 Characteristics of MDBS: Automatic generation of a unified global database schema from local databases.Provision of cross-database functionality by using unified schemata.Integration of heterogeneous database systems with multiple databases.Integration of data typesProvision of uniform but diverse set of interfaces to access and manipulate local data.
22 Open Data Base Connectivity ODBC is an application programming interface that provides solutions to the multi database programming.ODBC and other APIs provide standard database access through a common client-side interface.
23 Designing access layer classes Creating access layer is to create a set of classes that know hoe to communicate with the places where the actual data resides.The access layer must be able to translate the data request from the business layer into protocol for data access.Also retrieved data into the business layer format.In three tier architecture,The view layer : clientBusiness layer: application serverAccess layer: data base
24 Two major tasks:Translate the request: able to translate the data request from the business layer into protocol for data access.Translate the result: Also retrieved data into the business layer format
25 processMirror the business class package. For every identified business class, create one access class in access layer package.Define relationship. The same rule among business classes applies to access classes.Simplify classes and relationships. Eliminate unnecessary and redundant classes. Also combine simple classes and simplify super-sub class structure.3.1 redundant classes: select only one class if more than one classes provides same service.3.2 method classes: revisit the classes that consists of only one or two methods , if they can be eliminated or combined.4. Iterate and refine