HIM 502 Chapter 25

It may be divided into ___ transparency and ____ transparency.

- location -naming

___ constitute that subset of system states that causes the failure. __ is the cause of an error.

-Errors -Fault

___ is broadly defined as the probability that a system is running (not down) at a certain time point, whereas __ is the probability that the system is continuously available during a time interval.

-Reliability -availability

A distributed database (DDB) is a collection of multiple logically related database distributed over a ____, and a distributed _____ as a software system that manages a distributed database while making the distribution transparent to the user.

-computer network -database management system

■Other transparencies include __ transparency and ___ transparency—referring to freedom from knowing how the distributed database is designed and where a transaction executes.

-design -execution

If all servers (or individual local DBMSs) use identical software and all users (clients) use identical software, the DDBMS is called ____; otherwise, it is called ____.

-homogeneous -heterogeneous

The sites may all be located in physical proximity—say, within the same building or a group of adjacent buildings—and connected via a _____, or they may be geographically distributed over large distances and connected via a long-haul or ___.

-local area network -wide area network

In the three-tier client-server architecture, the following three layers exist: ______. This layer programs the application logic. example: queries formulated

Application layer (business logic)

___ determines the extent to which individual nodes or DBs in a connected DDB can operate independently.

Autonomy

___ autonomy of a component DBS refers to its ability to decide whether to communicate with another component DBS.

Communication

____ autonomy determines the extent to which each node can decide on sharing of information with other nodes.

Communication

_____ reduces the contention for CPU and I/O services and simultaneously reduces access delays involved in wide area networks.

Data localization

■ _______ (also known as distribution or network transparency). This refers to freedom for the user from the operational details of the network and the placement of the data in the distributed system. It may be divided into location transparency and naming transparency.

Data organization transparency

___ autonomy refers to independence of data model usage and transaction management techniques among nodes..

Design

Enterprises are using various forms of software—typically called the middleware, or Webbased packages called application servers (for example, WebLogic or WebSphere) and even generic systems, called _____ systems (for example, SAP, J. D. Edwards ERP)—to manage the transport of queries and transactions from the global application to individual databases (with possible additional processing for business rules) and the data from the heterogeneous database servers to the global application.

Enterprise Resource Planning (ERP)

___ autonomy refers to the ability of a component DBS to execute local operations without interference from external operations by other component DBSs and its ability to decide the order in which to execute them.

Execution

____ autonomy refers to independence of users to act as they please.

Execution

■_____ transparency. Two types of ____ are possible. _____ transparency makes the user unaware of the existence of fragments.

Fragmentation

___ fragmentation distributes a relation (table) into sub relations that are subsets of the tuples (rows) in the original relation.

Horizontal

___ transparency refers to the fact that the command used to perform a task is independent of the location of the data and the location of the node where the command was issued.

Location

For a database to be called distributed, the following minimum conditions should be satisfied: ■______ of the connected databases. It is essential that the information in the databases be logically related.

Logical interrelation

___ transparency implies that once a name is associated with an object, the named objects can be accessed unambiguously without additional specification as to where the data is located.

Naming

In the three-tier client-server architecture, the following three layers exist: ______. This provides the user interface and interacts with the user. The programs at this layer present Web interfaces or forms to the client in order to interface with the application.

Presentation layer (client)

___ and ___ are two of the most common potential advantages cited for distributed databases.

Reliability and availability

To achieve the potential advantages listed previously, the DDBMS software must be able to provide the following functions in addition to those of a centralized DBMS: ■____ data management. The ability to decide which copy of a ___ data item to access and to maintain the consistency of copies of a ___ data item.

Replicated

■___ transparency. Copies of the same data objects may be stored at multiple sites for better availability, performance, and reliability. ___ transparency makes the user unaware of the existence of these copies.

Replication

To achieve the potential advantages listed previously, the DDBMS software must be able to provide the following functions in addition to those of a centralized DBMS: ■__. Distributed transactions must be executed with the proper management of the __ of the data and the authorization/access privileges of users.

Security

____ occurs when there are differences in the meaning, interpretation, and intended use of the same or related data.

Semantic heterogeneity

There are two main types of multiprocessor system architectures that are commonplace: ■___ (loosely coupled) architecture. Multiple processors share secondary (disk) storage but each has their own primary memory.

Shared disk

There are two main types of multiprocessor system architectures that are commonplace: ■____ (tightly coupled) architecture. Multiple processors share secondary (disk) storage and also share primary memory.

Shared memory

semantic heterogeneity- The design autonomy of component DBSs refers to their freedom of choosing the following design parameters, which in turn affect the eventual complexity of the FDBS: ■___ and ___ constraints. These deal with serializability criteria, compensating transactions, and other transaction policies.

Transaction and policy

____ fragmentation distributes a relation into subrelations where each subrelation is defined by a subset of the columns of the original relation.

Vertical

Distributed databases are different from Internet Web files. ___ are basically a very large collection of files stored on different nodes in a network—the Internet—with interrelationships among the files represented via hyperlinks.

Web pages

The technology is, however, moving in a direction such that distributed ____ databases will become a reality in the future.

World Wide Web (WWW)

The ____ autonomy of a component DBS implies that it has the ability to decide whether and how much to share its functionality (operations it supports) and resources (data it manages) with other component DBSs.

association

Just as providing the ultimate transparency is the goal of any distributed database architecture, local component databases strive to preserve ___.

autonomy

The main thing that all such systems have in common is the fact that data and software are distributed over multiple sites connected by some form of _____.

communication network

The global query ___ references the global conceptual schema from the global system catalog to verify and impose defined constraints.

compiler

Federated Database Management Systems Issues: ■Differences in ___. ___ facilities for specification and implementation vary from system to system.

constraints

When the data and DDBMS software are distributed over several sites, one site may fail while other sites ______. Only the data and software that exist at the failed site cannot be accessed. This improves both reliability and availability.

continue to operate

A high degree of autonomy is desirable for increased flexibility and ____ of an individual node.

customized maintenance

In the case of a traditional centralized database, transparency simply pertains to logical and physical ____ for application developers.

data independence

Federated Database Management Systems Issues: ■Differences in ____. Databases in an organization come from a variety of data models, including the so-called legacy models, the relational data model, the object data model, and even files.

data models

For a database to be called distributed, the following minimum conditions should be satisfied: ■Connection of ____ over a computer network. There are multiple computers, called sites or nodes. These sites must be connected by an underlying communication network to transmit data and commands among sites

database nodes

The first factor we consider is the ____ of the DDBMS software.

degree of homogeneity

On the other hand, if____ by local transactions to a server is permitted, the system has some degree of local autonomy.

direct access

To achieve the potential advantages listed previously, the DDBMS software must be able to provide the following functions in addition to those of a centralized DBMS: ■Distributed ____ management. A ___ contains information (metadata) about data in the database. The ___ may be global for the entire DDB, or local for each site. The placement and distribution of the ___ are design and policy issues.

directory (catalog)

semantic heterogeneity- The design autonomy of component DBSs refers to their freedom of choosing the following design parameters, which in turn affect the eventual complexity of the FDBS: ■The universe of ___ from which the data is drawn..

discourse

A ______ processes Unit of execution (a transaction) in a distributed manner.

distributed database (DDB)

The term ______ can describe various systems that differ from one another in many respects.

distributed database management system

Improved ___ and ___ of application development. Developing and maintaining applications at geographically distributed sites of an organization is facilitated owing to transparency of data distribution and control.

ease and flexibility

Easier ____. In a distributed environment, ___ of the system in terms of adding more data, increasing database sizes, or adding more processors is much easier.

expansion

A ___ can be described as a deviation of a system's behavior from that which is specified in order to ensure correct execution of operations.

failure

To construct a system that is reliable, we can adopt several approaches. One common approach stresses ____ ; it recognizes that faults will occur, and designs mechanisms that can detect and remove faults before they can result in a system failure.

fault tolerance

We can directly relate reliability and availability of the database to the __,__ and __ associated with it.

faults, errors, and failures

The term _____ is used when there is some global view or schema of the federation of databases that is shared by the applications

federated database system (FDBS)

Organizations resort to distributed database management for various reasons. Some important advantages are listed below.

following are advantages to distributed databases - understand

The GCS, LCS, and their underlying mappings provide the ___ and ____ transparency

fragmentation and replication

the _____, which provides network transparency

global conceptual schema (GCS)

For a database to be called distributed, the following minimum conditions should be satisfied: ■Absence of ____ constraint among connected nodes. It is not necessary that all nodes be identical in terms of data, hardware, and software.

homogeneity

Local area networks typically use wireless ___ or ___, whereas long-haul networks use telephone lines or satellites.

hubs or cables

Moreover, ____ and ____ parallelism can be achieved by executing multiple queries at different sites, or by breaking up a query into a number of subqueries that execute in parallel.

interquery and intraquery

The latter is particularly important in queries involving ___.

joins

Another factor related to the degree of homogeneity is the degree of _____.

local autonomy

The logical organization of data at each site is specified by the _____.

local conceptual schema (LCS)

To accommodate potential heterogeneity in the DDB, each node is shown as having its own ____based on physical organization details at that particular site.

local internal schema (LIS)

Typical five-level schema architecture to support global applications in the FDBS environment is shown in Figure 25.6. In this architecture, the ____ is the conceptual schema (full database definition) of a component database, and the component schema is derived by translating the ___ into a canonical data model or common data model (CDM) for the FDBS.

local schema

Each local DBMS would have their local query optimizer, transaction manager, and execution engines as well as the local system catalog, which houses the ___.

local schemas

Having computed the cost for each candidate, the optimizer selects the candidate with the ____ for execution.

minimum cost

On the other hand, a ____ has full local autonomy in that it does not have a global schema but interactively constructs one as needed by the application

multidatabase system

These architectures enable processors to communicate without the overhead of exchanging messages over a ___..

network

A transaction can be executed by multiple ____ computers in a unified manner.

networked

If there is no provision for the local site to function as a standalone DBMS, then the system has __ local autonomy.

no

In shared nothing multiprocessor systems, there is symmetry and homogeneity of ___; this is not true of the distributed database environment where heterogeneity of hardware and operating system at each ___ is very common.

nodes

Management of distributed data with different levels of transparency:  This refers to the physical placement of data (files, relations, etc.) which is ___ to the user (distribution transparency).

not known

Database management systems developed using the above types of architectures are termed ____ database management systems rather than DDBMSs, since they utilize parallel processor technology.

parallel

Shared nothing architecture is also considered as an environment for ___ databases.

parallel

Improved ____. A distributed DBMS fragments the database by keeping the data closer to where it is needed most.

performance

Another more stringent approach attempts to ensure that the final system does not contain any faults. This is done through an exhaustive design process followed by extensive ____ control and testing.

quality

When a large database is distributed over multiple sites, smaller databases exist at each site. As a result, local ___ and __ accessing data at a single site have better performance because of the smaller local databases.

queries and transactions

Federated Database Management Systems Issues: ■Differences in ___. Even with the same data model, the languages and their versions vary.

query languages

The global ____ references both global and local conceptual schemas and generates optimized local queries from global queries. It evaluates all candidate strategies using a cost function that estimates cost based on response time (CPU,I/O, and network latencies) and estimated sizes of intermediate results.

query optimizer

To achieve the potential advantages listed previously, the DDBMS software must be able to provide the following functions in addition to those of a centralized DBMS: ■Distributed ____. The ability to access remote sites and transmit queries and data among the various sites via a communication network.

query processing

Federated Database Management Systems Issues: example- Even if two databases are both from the RDBMS environment, the same information may be represented as an attribute name, as a relation name, or as a value in different databases. This calls for an intelligent ___ mechanism that can relate information based on metadata.

query-processing

To achieve the potential advantages listed previously, the DDBMS software must be able to provide the following functions in addition to those of a centralized DBMS: ■Distributed database ___. The ability to recover from individual site crashes and from new types of failures, such as the failure of communication links.

recovery

A DDBMS ____ has to deal with failures arising from transactions, hardware, and communication networks.

recovery manager

Increased ___ and ___. This is achieved by the isolation of faults to their site of origin without affecting the other databases connected to the network.

reliability and availability

semantic heterogeneity- The design autonomy of component DBSs refers to their freedom of choosing the following design parameters, which in turn affect the eventual complexity of the FDBS: The ___ and ___of data elements and the structure of the data model may be prespecified for each local database.

representation and naming

Easier expansion (____)

scalability

Another type of multiprocessor architecture is called ____. In this architecture, every processor has its own primary and secondary (disk) memory, no common memory exists, and the processors communicate over a highspeed interconnection network (bus or switch).

shared nothing architecture

Federated Database Management Systems Issues: The modeling capabilities of the models vary. Hence, to deal with them uniformly via a single global schema or to process them in a ___ is challenging.

single language

semantic heterogeneity- The design autonomy of component DBSs refers to their freedom of choosing the following design parameters, which in turn affect the eventual complexity of the FDBS: ■The understanding, meaning, and _____ of data. This is a chief contributor to semantic heterogeneity.

subjective interpretation

semantic heterogeneity- The design autonomy of component DBSs refers to their freedom of choosing the following design parameters, which in turn affect the eventual complexity of the FDBS: ■Derivation of ___. Aggregation, summarization, and other dataprocessing features and operations supported by the system.

summaries

Networks may have different ___ that define the direct communication paths among sites. The type and ___ of the network used may have a significant impact on the performance and hence on the strategies for distributed query processing and distributed database design.

topologies

To achieve the potential advantages listed previously, the DDBMS software must be able to provide the following functions in addition to those of a centralized DBMS: ■Keeping ___of data distribution. The ability to keep ___ of the data distribution, fragmentation, and replication by expanding the DDBMS catalog..

track

To achieve the potential advantages listed previously, the DDBMS software must be able to provide the following functions in addition to those of a centralized DBMS: ■Distributed ____. The ability to devise execution strategies for queries and transactions that access data from more than one site and to synchronize the access to distributed data and maintain the integrity of the overall database.

transaction management

The global ____ is responsible for coordinating the execution across multiple sites in conjunction with the local ____ at those sites.

transaction manager

In addition, each site has a smaller number of ___executing than if all ___ are submitted to a single centralized database.

transactions

The concept of ____ extends the general idea of hiding implementation details from end users.

transparency

A highly transparent system offers a lot of flexibility to the end user/application developer since it requires little or no awareness of ____ on their part.

underlying details