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Distributed DBMS Architecture Chapter 4 Principles Of Distributed Database Systems,2/e By Ozsu, Patrick Valduriez Distributed DBMS Architecture Architecture of a systems defines its structure, means, the components of the systems, function performed by each component and the relationship among components BZUPAGES.COM • Three major architectures of DDBMS discussed –Peer to peer –Client/Server –Multdatabase • These are idealized architectures, practical installations may wary BZUPAGES.COM DBMS Standardization A conceptual framework whose purpose is to divide standardization work into manageable pieces and to show at a general level how these pieces are related to one another. Approaches BZUPAGES.COM • Component-based Components of the system are defined together with the interrelationships between components. Good for design and implementation of the system. However it is difficult to determine functionality of system by seeing its individual component BZUPAGES.COM • Function-based Classes of users are identified together with the functionality that the system will provide for each class. The objectives of the system are clearly identified. But how do you achieve these objectives? BZUPAGES.COM • Data-based Identify the different types of describing data and specify the functional units that will realize and/or use data according to these views BZUPAGES.COM Practically • Every aspect has to be considered • These Classification schemes are Orthogonal • A committee for the DBMS standardization was established in 1972 by ANSI under SPARC (Standards Planning and Requirement Committee) BZUPAGES.COM • Published its initial report in 1975 and then in 1977 • Its full name being “ANSI/X3/SPARC DBMS Framework” • Mainly based on Data organization BZUPAGES.COM Reference Model Users External Schema External View Conceptual Schema Internal Schema BZUPAGES.COM External View Conceptual View Internal View External View Dimensions for DDBS Architecture Autonomy refers to the distribution of control not of data. It indicates the degree to which individual DBMSs can operate independently. Types could be Design, Communication and Execution Autonomy. Degree of Autonomy varies in different DDBS architectures BZUPAGES.COM Distribution deals with data. Logically, data appears to be placed at a single place but practically it may be spread at physically different locations BZUPAGES.COM Heterogeneity refers the differences in hardware and software among the individual databases. Like different machines, OS, Data Models, DBMSs, or query languages BZUPAGES.COM BZUPAGES.COM Major DDBS Architectures-I 1.Client-Server Architecture – The term used in different meanings; generally C and S refer to processes, may be running at the same machines – In the context of DDBS both client and server are machines not processes (Fig 4.4) – Server performs most of the data Management; • Query Processing BZUPAGES.COM • Transaction and Storage Management Major DDBS Architectures-I & II –Client passes user queries to server without trying to understand or optimize them –One Server Multiple Clients –Multiple Servers • One Server at a time • Multiple Servers (transparently) at a time (A DDBS) 2- Peer to Peer Distributed Systems • Heterogeneous databases at each site, defining Local Internal Schemas BZUPAGES.COM Interpreting user commands and formats results Checks if user query can be processed Optimized execution strategy Global queries to local ones Coordinates distribution execution of user requests BZUPAGES.COM Chooses best access path to any data item Makes sure the consistency of local data even in case of failure Physically accesses the data as per the commands generated by query optimizer. Interacts with the OS BZUPAGES.COM Major DDBS Architectures-III A Multidatabase System • Provides access from multiple, autonomous heterogeneous, and distributed databases. Two Major architectures: • • Global Schema Architecture Federated Schema Architecture BZUPAGES.COM Multidatabase Systems: Architectures External Schema External Schema External Schema External Schema Federated Schema Global Schema Federated Schema Schema Integration Export Schema Component Schema ••• Export Schema Export Schema Export Schema Component Schema Component Schema ••• Component Schema Schema Translation Local Schema Local Schema ••• Global Schema Architecture BZUPAGES.COM Local Schema Local Schema ••• Federated Database Architecture Global Directory Issues • A directory is a database that contains data about data (meta-data). Called global directory in case of a DDBS. Three issues; • A single large or local for each site • Location; whether to keep at a single site or distributed. • Single copy or replication • All three issues are orthogonal to each other • That concludes chapter 4, questions? BZUPAGES.COM Distributed database environments (adapted from Bell and Grimson, 1992) BZUPAGES.COM Distributed Database Options • Homogeneous - Same DBMS at each node. – Autonomous - Independent DBMSs. – Non-autonomous - Central , coordinating DBMS. • Heterogeneous - Different DBMSs at different nodes. – Gateways - Simple paths are created to other databases without the benefits of one logical database. BZUPAGES.COM Distributed Database Options – Systems - Supports some or all of the functionality of one logical database. • Full DBMS Functionality - All dist. Db functions. • Partial-Multi-database - Some dist. Db functions. –Federated - Supports local databases for unique data requests. » Loose Integration - Local dbs have their own schemas. » Tight Integration - Local dbs use common schema. –Unfederated - Requires all access to go through a central, coordinating module. BZUPAGES.COM Homogeneous, NonAutonomous Database • Data is distributed across all the nodes. • Same DBMS at each node. • All data is managed by the distributed DBMS (no exclusively local data.) • All access is through one, global schema. • The global schema is the union of all the local schema. BZUPAGES.COM Focus on The Following Heterogeneous Environment • Data distributed across all the nodes. • Different DBMSs may be used at each node. • Local access is done using the local DBMS and schema. • Remote access is done using the global schema. BZUPAGES.COM