DBMS Interview osakeya.info - Download as PDF File .pdf), Text File .txt) or read online. If you would like to view All All DBMS interview questions only, at one place, visit dbms interview questions with answers pdf, interview questions for dbms. Technical interview questions and answers section on "DBMS Basics" with freshers can download DBMS Basics quiz questions with answers as PDF files and.
|Language:||English, Spanish, Hindi|
|Genre:||Science & Research|
|Distribution:||Free* [*Registration Required]|
Commonly asked DBMS interview questions | Set 1. What are advantages of DBMS Source: osakeya.info Wisdomjobs has interview questions which are exclusively designed for job seekers to assist them in clearing job interviews. DBMS+RDBMS interview. + Dbms Interview Questions and Answers, Question1: What is a DBMS? Question2: What is Relationship set? Question3: What is Relationship type?.
A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more. What is 1 NF Normal Form? The domain of attribute must include only atomic simple.
What is 2NF? X must be a candidate key. It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition. What is 3NF? Partial Key: It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. X is a super key. Binary search style indexing B-Tree indexing Inverted list indexing Memory resident table Table indexing The join dependency is implied by the set of FD.
What are partial. Natural Key: When one of the data elements stored within a construct is utilized as the primary key. What is 5NF? What is indexing and what are the different kinds of indexing? Indexing is a technique for determining how quickly specific data can be found. Compound Key: If no single data element uniquely identifies occurrences within a construct. Alternate Key: What is system catalog or catalog relation?
How is better known as? Then this is known as developing an artificial key. Artificial Key: If no obvious key. What is Domain-Key Normal Form?
A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation. It is sometime called as Discriminator. It is used when we need to express a relationship among relationships. Analysis phase. What is a Phantom Deadlock? In distributed deadlock detection.
By taking checkpoints. What is a checkpoint and When does it occur? DBMS ensures this by undoing the actions of incomplete transactions. What is meant by query optimization? The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.
Users should not have to worry about the effect of incomplete transactions. What are the different phases of transaction? Different phases are 1. A concept which is used to model a relationship between a collection of entities and relationships. Such situations are called phantom deadlocks and they lead to unnecessary aborts. What is durability in DBMS? Once the DBMS informs the user that a transaction has successfully completed.
It is also called data dictionary. Undo phase. This information is stored in a collection of relations maintained by the system called metadata.
What do you mean by flat file database? Redo Phase. What do you mean by atomicity and aggregation? This property is called durability. Either all actions are carried out or none are. What is a query? A query with respect to DBMS relates to user commands that are used to interact with a data base. Name the buffer in which all the commands that are typed in are stored? What are the unary operations in Relational Algebra? Columns from the subquery cannot be referenced anywhere else in the parent query.
The query language can be classified into data definition language and data manipulation language. It has no crossfile capabilities but is user-friendly and provides user-interface management. CNUM What are the primitive operations common to all record management systems? The following example demonstrates a non-correlated subquery. A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause.
If the subquery is executed for each row of the parent. Depending on how the subquery is written. What is "transparent DBMS"? It is one. What do you mean by Correlated subquery? Transaction Control. Language Processing. Logging and Recovery. Name the three major set of files on disk that compose a database in Oracle. The primary difference between SQL and other conventional programming languages is that SQL statements specify what data operations should be performed rather than how to perform them.
Concatenation of every row in one relation with every row in another. Storage Management. SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. Memory Management. Data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel.
Lock Management. Process Control. What is the job of the information stored in data-dictionary? The information in the data dictionary validates the existence of the objects. Distribution Control. Concatenation of rows from one relation and related rows from another. The trigger can e defined to execute once for the entire statement or once for every row that is inserted.
For any one table. What is Transaction Manager? It is a program module. Without these files. What is Buffer Manager? Database files 2. These are 1. What is database Trigger? All the files are binary. The control files and the redo logs support the functioning of the architecture itself. Redo logs The most important of these are the database files where the actual data resides.
Control files 3. A stored procedure can have a set of compound SQL statements. All three sets of files must be present. What is Storage Manager?
It is a program module that provides the interface between the low-level data stored in database. What are stored-procedures? And what are the advantages of using them?
Stored procedures are database objects that perform a user defined operation. A stored procedure executes the SQL commands and returns the result to the client. Stored procedures are used to reduce network traffic. You must shut down the instance to guarantee a consistent copy. What is Authorization and Integrity manager? It is the program module. What are stand-alone procedures? Procedures that are not part of a package are known as stand-alone because they independently defined. The language supports the use two types of cursors 1.
Explicit What is cold backup and hot backup in case of Oracle? This is a straight file copy. Implicit 2. Retroactive Update: The updates that are applied to database after it becomes effective in real world. Another limitation of stand-alone procedures is that they are compiled at run time.
If a cold backup is performed. What are cursors give different types of cursors? These types of procedures are not available for reference from other Oracle tools. What is File Manager? The cold backup is not an available option. What is meant by Proactive. Hot Backup: Some sites such as worldwide airline reservations systems cannot shut down the database while making a backup copy of the files.
Cold Backup: It is copying the three sets of files database files. All work performed on the database since the last backup is lost. Retroactive and Simultaneous Update. Proactive Update: The updates that are applied to database before it becomes effective in real world. Simulatneous Update: The updates that are applied to database at the same time when it becomes effective in real world. Flag for inappropriate content. Related titles.
Description and Taxonomy of the Manufacturing Processes. Jump to Page. Search inside document. Rhenielou Cristobal. Bhupesh Gupta. Eby Johnson C. Karthy R Ramamurthi. Sopno Nondita. Kaushik Sadhu. Dino Bektas. Avdhesh Gupta. Thota Mahesh Dba. Pushpendra Patel. Diego Akechi. Karthik Krishnaswamy. Tolulope Abiodun. More From ssambangi Saurabh Deshmukh. What Is "transparent Dbms"? It is one, which keeps its Physical Structure hidden from user. What Is A Query? A query with respect to DBMS relates to user commands that are used to interact with a data base.
The query language can be classified into data definition language and data manipulation language. Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery. A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause.
Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery. Concatenation of every row in one relation with every row in another. Concatenation of rows from one relation and related rows from another.
What Is Rdbms Kernel? Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database You might think of an RDBMS as an operating system or set of subsystems , designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures.
Data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel. The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location. SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. The primary difference between SQL and other conventional programming languages is that SQL statements specify what data operations should be performed rather than how to perform them.
There are three major sets of files on disk that compose a database. All the files are binary. These are 1. Database files 2. Control files 3. Redo logs The most important of these are the database files where the actual data resides. The control files and the redo logs support the functioning of the architecture itself. All three sets of files must be present, open, and available to Oracle for any data on the database to be useable.
Without these files, you cannot access the database, and the database administrator might have to recover some or all of the database using a backup, if there is one. What Is Database Trigger? The trigger can e defined to execute once for the entire statement or once for every row that is inserted, updated, or deleted.
For any one table, there are twelve events for which you can define database triggers. What Are Stored-procedures? Stored procedures are database objects that perform a user defined operation. A stored procedure can have a set of compound SQL statements. A stored procedure executes the SQL commands and returns the result to the client. Stored procedures are used to reduce network traffic. What Is Storage Manager? It is a program module that provides the interface between the low-level data stored in database, application programs and queries submitted to the system.
What Is Buffer Manager? It is a program module, which is responsible for fetching data from disk storage into main memory and deciding what data to be cache in memory. What Is Transaction Manager? It is a program module, which ensures that database, remains in a consistent state despite system failures and concurrent transaction execution proceeds without conflicting.
What Is File Manager? It is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.
It is the program module, which tests for the satisfaction of integrity constraint and checks the authority of user to access data. What Are Stand-alone Procedures? Procedures that are not part of a package are known as stand-alone because they independently defined.
These types of procedures are not available for reference from other Oracle tools. Another limitation of stand-alone procedures is that they are compiled at run time, which slows execution.
The language supports the use two types of cursors 1. Implicit 2. Cold Backup: It is copying the three sets of files database files, redo logs, and control file when the instance is shut down.
This is a straight file copy, usually from the disk directly to tape. You must shut down the instance to guarantee a consistent copy. If a cold backup is performed, the only option available in the event of data file loss is restoring all the flies from the latest backup. All work performed on the database since the last backup is lost. Hot Backup: Some sites such as worldwide airline reservations systems cannot shut down the database while making a backup copy of the files.
The cold backup is not an available option. What is meant by Proactive, Retroactive and Simultaneous Update. Proactive Update: The updates that are applied to database before it becomes effective in real world. Retroactive Update: The updates that are applied to database after it becomes effective in real world. Simultaneous Update: The updates that are applied to database at the same time when it becomes effective in real world.
Data is recorded facts and figures, and information is knowledge derived from data. A database stores data in such a way that information can be created. Enterprise Resource Planning ERP is an information system used in manufacturing companies and includes sales, inventory, production planning, downloading and other business functions.
An ERP system typically uses a multiuser database. Who Is E. While working at IBM, E. Codd created the relational database model. A paper he published in presented his ideas to the world at large. His work is the foundation for most of the DBMSs currently in use, and thus forms the basis for database systems as we know and use them today. SQL stands for Structured Query Language, and is the most important data processing language in use today.
It is not a complete programming language like Java or C , but a data sublanguage used for creating and processing database data and metadata. What Is An Sql Subquery? An SQL subquery is a means of querying two or more tables at the same time. Some subqueries have equivalent SQL join structures, but correlated subqueries cannot be duplicated by a join.. Relations are also called tables, and sometimes by the older data processing term files.
A row is known as a tuple in the relational model, but may also be referred to as a record. Finally, relational model attributes are known as table columns and sometimes as fields.
Equations deal with numerical relationships. A functional dependency deals with the existence of a determinant relationship between attributes, regardless of whether or not there is a numerical relationship between them. Thus, if we know that there is no hot water every Wednesday, No-Hot-Water is functionally dependent on Wednesday.
So, if we know it is Wednesday, then we know we will have No-Hot-Water. This is a functional dependency, but not an equation. A foreign key is used to establish relationships among relations in the relational model. Technically, a foreign key is a column or columns appearing in one relation that is are the primary key of another table. Although there may be exceptions, the values in the foreign key columns usually must correspond to values existing in the set of primary key values. This correspondence requirement is created in a database using a referential integrity constraint on the foreign key.
A deletion anomaly occurs when, by deleting the facts about one entity, we in advertently delete facts about another entity; with one deletion, we lose facts about two entities. An insertion anomaly happens when we encounter the restriction that we cannot insert a fact about one entity until we have an additional fact about another entity.
Multivalued dependencies, Functional dependencies, Candidate keys, Primary keys and Foreign keys. Tables that are normalized contain data that has been distributed among the tables, but which may need to be recombined to answer queries from an application. The inconsistent values problem occurs when different users or data sources use slightly different forms of the same data value. Entities of a given type are grouped into entity classes. An entity instance is the representation of a particular entity.
Entities have attributes. Entity instances have identifiers. Identifiers are attributes that name, or identify, entity instances. N - a single entity instance of one type is related to many-entity instances of another type. N - many-entity instances of one type relate to many-entity instances of another type. The ideal primary key is short, numeric and fixed. A surrogate key is a unique, DBMS-supplied identifier intended to be used as the primary key of a table. Further, the DBMS will not allow the value of a surrogate key to be changed.
The values of a surrogate key have no meaning to the users and are usually hidden on forms and reports. By design, they are short, numeric and fixed and thus meet the definition of the ideal primary key. Define And Discuss Data Constraints? Data constraints on a column are the limits put on the values the data can have. A recursive relationship is a relationship among entities of the same class, and is represented in the same way as other relationships are. The rows of the tables can take two different roles, however.
Some are parent rows, and others are child rows. Further, the table will contain both its own primary key and the foreign key that links back to the table itself. If a row has no parent, then the value of the foreign key column in that row will be null. If the row has a parent, then there must be a foreign key value in that row that corresponds to the primary key value of another row in the table. What Is A Cascading Update? Referential integrity constraints require that foreign key values in one table correspond to primary key values in another.
If the value of the primary key is changed -- that is, updated -- the value of the foreign key must immediately be changed to match it. Cascading updates will set this change to be done automatically by the DBMS whenever necessary. What Is A Sql View? A SQL view is a virtual table built from other tables or views. SQL statements return a set of rows, while an application program works on one row at a time.
To resolve this mismatch the results of SQL statements are processed as pseudofiles, using a cursor or pointer to specify which row is being processed. Name Four Applications For Triggers?
A stored procedure is a program that is stored within the database and is compiled when used. They can receive input parameters and they can return results.
Unlike triggers, their scope is database-wide; they can be used by any process that has permission to use the database stored procedure. The advantages of stored procedures are: Why Is Database Redesign Necessary? Database redesign is necessary for two reasons. First, redesign is necessary both to fix mistakes made during the initial database design.
Second, redesign is necessary to adapt the database to changes in system requirements. Such changes are common because information systems and organizations do not just influence each other they create each other.
Thus, new information systems cause changes in systems requirements. A complete backup makes a copy of the entire database. A differential backup makes a copy of the changes that have been made to the database since the last complete backup. A complete backup must be made before the first differential backup. Because differential backups are faster, they can be taken more frequently and the chance of data loss is reduced.
Complete backups take longer but are slightly simpler to use for recovery. With it, SQL Server places a range lock on the rows that have been read. This level is the most expensive to use and should only be used when absolutely required. With the simple recovery model, no logging is done. The only way to recover a database is to restore the database to the last backup.
With full recovery, all database changes are logged. With bulk-logged database recovery, all changes are logged except those that cause large log entries. With a clustered index, the data are stored in the bottom level of the index and in the same order as that index. With a nonclustered index, the bottom level of an index does not contain data; it contains pointers to the data. For data retrieval, clustered indexes are faster than nonclustered indexes.
An ODBC file data source is a file that can be shared among database users. A ODBC system data source is one that is local to a single computer. This is a large task that requires a substantial initial investment. An object need not expose all of its properties and methods in a given interface.
The implementation is completely hidden from the user. Thus developers of an object are free to change the implementation whenever they want, but they should not change the interface without consulting their users.
Symbols cannot be used ambiguously with XML. A document can be well-formed and not be type-valid, either because it violates the structure of its DTD or because it has no DTD.
Simple elements have only one data value. ComplexType elements can have multiple elements nested within them. ComplexTypes may also have attributes. The elements contained in a complexType may be simple or other complexTypes. ComplexTypes may also define element sequences. This creates a sequence that starts at one 1 and increases by one 2 for each new record. MySql maintain its metadata in a database named mysql. For example, this database maintains two tables named user and db.
What Is A Data Mart? A data mart Is a collection of data smaller In scope and size than a data warehouse. It is dedicated to data from a particular business component of business functional area.
A data mart may function as a subset of a larger data warehouse. Users of a data mart are usually knowledgeable analysts in the business area using the data mart.
A reporting system has three functions: Report authoring -- connecting to data sources, creating the report structure and formatting the report. Report management -- defining who receives which reports, when they receive them and how the reports are delivered.
Report delivery -- based on report management metadata, either pushing the reports to the recipients or allowing them to be pulled by the recipients. OLAP provides the user with the capability to sum, count, average and do other simple arithmetic operations on groups of data. An OLAP report has measures and dimensions. Measures are the data values to be displayed. Dimensions are characteristics of the measures. What Is Market Basket Analysis?
Market basket analysis is a data mining technique that determines which sets of products tend to be downloadd together. A common technique uses conditional probabilities. In addition to the basic probability that an item will be downloadd, three results are of particular interest: Support -- the probability of two items being downloadd together.
Confidence -- the probability of a second item being downloadd GIVEN that another item has been downloadd. Lift -- calculated as confidence divided by a basic probability, this shows the likelihood of a second item being downloadd IF an item is downloadd.
Structured data are facts concerning objects and events. The most important structured data are numeric, character, and dates. Structured data are stored in tabular form. Unstructured data are multimedia data such as documents, photographs, maps, images, sound, and video clips. Unstructured data are most commonly found on Web servers and Web-enabled databases.
Many businesses still use file processing systems today. This is especially true in the creation of backups for a database system. In addition, if you understand some of the limitations of a file processing system such as program-data dependence, duplication of data, limited data sharing, lengthy development times, and excessive program maintenance, you can try and avoid them as you design and develop a databases.
There are five disadvantages. Program-data dependence occurs when file descriptions need to be changed in all programs whenever a file description changes.
Duplication of data is storing the data more than one time. Limited data sharing occurs when the files are private so no one outside of one application can access the data. Lengthy development times exist because file processing systems takes longer to develop. Lastly, excessive program maintenance exists since the effort to maintain a program is larger in this environment. Explain The Five Different Categories? Databases can support from a single user personal database up to supporting the requests of the world internet database.
In between, a database can support a workgroup a relatively small group of people , department database a functional unit in an organization such as marketing , or an enterprise database entire organization. Universal data models are common to many organizations. These models may be useful for similar functions that are used across companies or organizations such as downloading and accounting. Industry-specific data models are used by specific industries.
Briefly Explain An Erd? An ERD is a detailed logical representation of the data for an organization. The ERD includes entities, attributes, relationships, and cardinalities. An ERD is the mechanism where an entity-relationship model is displayed. Definitions are gathered from the same sources and should be accompanied diagrams.
A definition will include special conditions, examples, how the data is created, whether the data can change, who owns the data, whether the data is optional, and whether the data can be broken into something more atomic. Explain Minimum And Maximum Cardinality?
Minimum cardinality is the minimum number of instances of an entity that can be associated with each instance of another entity. Maximum cardinality is the maximum number of instances of an entity that can be associated with each instance of another entity.
The values of data may change. A time stamp helps to ensure that the previous value of the data stays in the database after it has changed so that you can see the before and after values through time. Without a time stamp, you will most likely lose some of the history.
Total specialization exists when every instance of a supertype must also be an instance of a subtype. Partial specialization exists when every instance of a supertype does not have to be an instance of a subtype.
An EER allows for object-oriented data modeling and include supertypes and subtypes entities and inheritance. The disjoint rule states an entity instance of a supertype can only be a member of one subtype. The overlap rule states an entity instance of a supertype can be a member of multiple subtypes. A derivation is a statement that is derived from other knowledge. A structured assertion is a statement that expresses some aspect of the static structure of an organization.
An action assertion is a statement of a constraint on the actions of an organization. A scenario is used to test business rules. It is a short script that describes how a business reacts to certain situations. Normalization should minimize data redundancy.
It should also simplify referential integrity constraints. Normalization will also make it easier to insert, update, and delete data. And finally, it provides better design. Relations in a database have a unique name and no multivalued attributes exist. Each row is unique and each attribute within a relation has a unique name. The sequence of both columns and rows is irrelevant. First you must verify that a relation is in both first normal form and second normal form. If the relation is not, you must convert into second normal form.
After a relation is in second normal form, you must remove all transitive dependencies. A separate relation is created for each supertype and subtype. The attributes common for all of the subtypes are assigned to the supertype. Each subtype has the primary key from the supertype assigned to it.
A subtype discriminator is added to the supertype. Describe Domain Constraints? Domain constraints include entity integrity and referential integrity. The domain is a set of values that may be assigned to an attribute. The entity integrity rule states that no part of a primary key cannot be null. Referential integrity states that each foreign key value must match a primary key value or be null. A data type should be selected so that all possible values are represented using minimal storage space.
The data type should help to ensure data integrity and support all possible data manipulations i. Horizontal portioning is where the rows in a relation are separated by some criteria and placed into a new relation or file with the same layout as the original relation in this case only the records in each file differ. Vertical portioning is where the columns in a relation are separated by some criteria and placed into a new relation or file with a different layout as the original relation.
A dynamic view may be created every time that a specific view is requested by a user. A materialized view is created and or updated infrequently and it must be synchronized with its associated base table s.
Choosing primary and secondary keys can increase the speed of row selection, joining, and row ordering. Selecting the appropriate file organization for base tables and indexes can also improve performance.
Clustering related rows together and maintaining statistics about tables and indexes can lead to increased efficiency. Data definition language commands are used to create, alter, and drop tables. Data manipulation commands are used to insert, modify, update, and query data in the database. Data control language commands help the DBA to control the database. Identify the data type, length, and precision for each attribute. Identify primary and related foreign keys with the parent table being created before the child.
A standard language can hinder the effort to create a new language. One standard is never enough to meet all of the business needs.
A standard can be a compromise among interested parties which can cause the standard to not be ideal.
If a standard is altered by some, than portability between platforms could be hurt. Triggers are stored and controlled in the DBMS. A procedure is also stored in a database. A procedure is not executed automatically. Briefly Describe An Outer Join?
An outer join includes the records that match and those that do not have a matching value in another table. Outer joins are not easily used with more than two tables. Describe A Subquery? A subquery is a query that is composed of two queries. In some cases the inner query provides results for the outer query to process. In other cases, the outer query results provide results for the inner query correlated subquery.
These statements do not change unless the source code is modified. The statements generated do not have to be the same each time. A three-tier architecture includes a client and two server layers. The application code is stored on the application server and the database is stored on the database server.
A two-tier architecture includes a client and one server layer. The database is stored on the database server. QBE is a direct-manipulation database language that uses a graphical approach to query construction. ODBC is a standard that contains an interface that provides a common language for application programs to access and process SQL databases.
In order to use ODBC, a driver, server name, database name, user id, and password are required. ODBC is important for Internet applications and has gained wide acceptance. A fat client is a PC that is responsible where most processing occurs on the client rather than the server. Some of the fat client activities include processing, presentation logic, and business rules logic.
A thin client is a PC where only limited processing occurs. In these cases, more processing should occur on the application server. You can perform more complex functions and error handling can be accommodated by VBA. VBA code will execute faster since code runs faster than macros and maintenance is easier because VBA modules are stored with the forms and reports.
Reading VBA is easier because you can see the entire code. Finally, you can pass parameters and use OLE automation better. Both require the use of several files. Both use tags and are executed on the server. Both Internet Explorer and Netscape can access these files. The programmer does not need to be concerned with the client when they work with this middleware. Describe Web Services? Web Services are improving the ability of computers to communicate over the Internet. These services use XML programs and usually run in the background.
Easier integration of applications may be possible because developers do not need to be familiar with the technical details with applications that are being integrated. UDDI is a technical specification for creating a distributed registry of Web services and businesses that are open to communicating through Web services. Provide An Overview Of Xml?
XML Is used to structure and manipulate data involved with a browser and is becoming the standard for ec ommerce. Describe Website Security Issues? Security measures should include all aspects of the system such as the network, operating level, database, and Web server.
Describe A Data Warehouse? A data warehouse is organized around specific subjects. The data is defined using consistent naming, format, and encoding structure standards. The data contains a time element, so that the data can be studied for trends.
No data in a data warehouse can be updated by end users. One reason that an information gap exists is the fact that systems have been developed in separate, segmented efforts. This has helped the data from being stored in an integrated database and thus the data is in an inconsistent structure.
The other reason for the gap is that most systems are created to support the operational aspect of an organization. The systems were not developed for decision making.
A data warehouse is for the enterprise and contains multiple subjects. A data mart is for a specific functional area and focuses on one subject. A data warehouse is flexible and data-oriented and contains detailed historical data.