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Database Programming
Databases are collections of tables that maintain and display information, often collaboratively; this information can be used for interaction with an application or gaining general knowledge. Questions about database engines and modifying or using them belong in this category.
8,803 Questions
Problems that occur when incorrect data is stored?
There are quite a few problems with storing data
1) security issues
2) excessive data
A database is important because it stores a lot of information. This information can later be used in cases of emergency or reference.
A DBMS is typically shared among many users. Transactions from these users
can be interleaved to improve the execution time of users' queries. By interleaving
queries, users do not have to wait for other user's transactions to complete
fully before their own transaction begins. Without interleaving, if user A begins
a transaction that will take 10 seconds to complete, and user B wants to begin
a transaction, user B would have to wait an additional 10 seconds for user
A's transaction to complete before the database would begin processing user B's
request.
Explain the concepts of recoverable schedule in dbms?
Transactions commit only after all transactions whose changes they read, commit
Advantages of using indexes in database?
Advantages of an index over no index
If no index exists on a table, a table scan must be performed for each table referenced in a database query. The larger the table, the longer a table scan takes because a table scan requires each table row to be accessed sequentially. Although a table scan might be more efficient for a complex query that requires most of the rows in a table, for a query that returns only some table rows an index scan can access table rows more efficiently.
The optimizer chooses an index scan if the index columns are referenced in the SELECT statement and if the optimizer estimates that an index scan will be faster than a table scan. Index files generally are smaller and require less time to read than an entire table, particularly as tables grow larger. In addition, the entire index may not need to be scanned. The predicates that are applied to the index reduce the number of rows to be read from the data pages.
7 If an ordering requirement on the output can be 7 matched with an index column, then scanning the index in column order will 7 allow the rows to be retrieved in the correct order without a sort.
Each index entry contains a search-key value and a pointer to the row containing that value. If you specify the ALLOW REVERSE SCANS parameter in the CREATE INDEX statement, the values can be searched in both ascending and descending order. It is therefore possible to bracket the search, given the right predicate. An index can also be used to obtain rows in an ordered sequence, eliminating the need for the database manager to sort the rows after they are read from the table.
In addition to the search-key value and row pointer, an index can contain include columns, which are non-indexed columns in the indexed row. Such columns might make it possible for the optimizer to get required information only from the index, without accessing the table itself.
Note:The existence of an index on the table being queried does not guarantee an ordered result set. Only an ORDER BY clause ensures the order of a result set.
Example of multiple relationship between entities?
bascially, i dont know thr answer myself. so i am waiting for someone to upload it. hurry yeah, i need to finish my assignment off.
thank you
What are limitations of object oriented database model?
- Schema Changes: In an RDBMS modifying the database schema either by creating, updating or deleting tables is typically independent of the actual application. In an OODBMS based application modifying the schema by creating, updating or modifying a persistent class typically means that changes have to be made to the other classes in the application that interact with instances of that class. This typically means that all schema changes in an OODBMS will involve a system wide recompile. Also updating all the instance objects within the database can take an extended period of time depending on the size of the database.
- Language Dependence: An OODBMS is typically tied to a specific language via a specific API. This means that data in an OODBMS is typically only accessible from a specific language using a specific API, which is typically not the case with an RDBMS.
- Lack of Ad-Hoc Queries: In an RDBMS, the relational nature of the data allows one to construct ad-hoc queries where new tables are created from joining existing tables then querying them. Since it is currently not possible to duplicate the semantics of joining two tables by "joining" two classes then there is a loss of flexibility with an OODBMS. Thus the queries that can be performed on the data in an OODBMS is highly dependent on the design of the system.
What does record mean in relation to databases?
it when you see your first name/ last name, date of birth school if you think about it you have your first name in one column and DOB (date of birth) in one and last name in the other it is set. It is just a database which is filled with important or
essential information
hope that helps so good look if your learning about databases or for homework.
Differences between hand file and flat file?
The original answer was "difference between flat file and hand file". Not an answer, only repeats the question.
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[ This question seems to have been placed, originally, in the wrong category: Database Programming. It contains the term "flat file", which does make it seem to be a computer item, but flat file can also refer to a type of hand tool. The fact that the question deals with the difference between a hand file and a flat file, two varieties of a common hand tool, makes it clear that this question should be in a category addressing tools in general, and hand tools in particular.
It may be that the person asking the question thought "hand file" referred to a type of computer storage file, and thus placed the question in what he thought was the appropriate category. My answer addresses the two terms as they relate to metal or wood working, so I copied the question (and answer) to the only existing category that fits: Building and Carpentry. I wish there were a separate category under Home and Garden for just "Tools", but there isn't, so I chose Building and Carpentry. In doing so, I may be just confusing the issue. I hope I didn't, and if I did, I'm sorry. OffGrid9 ]
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A hand file is rectangular in cross section, parallel in both width and thickness from end to end. One edge (the "safe edge" has no teeth, allowing a user to file one surface right up to the edge in a corner without marring the other surface. In recent years, it is common to find hand files that taper in thickness, but the width is still parallel.
A flat file is similar to a hand file. It is also rectangular in cross section, but it tapers in both thickness and width, and it does not have a safe edge. In older flat files, the width was usually parallel for most of the file's length, then curved near the end to taper in. On modern flat files, the width usually tapers in throughout the file's length - the sides may curve, the taper increasing towards the end, or the sides may be straight, with the taper being continuous from end to end.
Difference between dB dBm and dBi?
dB or dBW relativ to 1W
: dBm for dB relativ to 1 milliwatt. 0 dBm= 1 mW = -30dBW
.
Its interesting,but these terms are used interchangeably at times, erroneously.The term dBm is used by
communications engineers and it is absolute.Most Power meters commercially available have this scale.
It is : dBm=10log(base 10)(P1/P2) at two different Power points.Power is read always across a 50 Ohm
resistor.IEEE has made this a standard and 1mW=0dBm(-40dBm is 100nW accross 50 Ohm and +20dBm is 100mW).
As far as I know dB(not DB)refers simly to gain(and loss/attenuation as -dB).It is different this time
as the equation is not Power but a simple ratio: dB=20log(base 10)(Gain or attenuation).One can have
a reference and above that reference he is talking in positive dBs(Gain) and below in negative dBs(loss
or attenuation).Such scales can then be modified as we have done for Acoustic Emission where we talk in
dBae and our refence is the "perfect" sensor giving us ONLY 1microVolt(!) Peak output noise.Anyway a
good goal.So for 40dBae a sensor/Amplifier(40dB Gain)output across a 50 Ohm resistor is 10mV.
What does it mean When your internal antivirus database is out of date?
That the virus definition of your anti-virus software need to be updated.
What is the characteristics of dbms?
Basic Characteristics of DBMS
• Represents complex relationship between data
• Controls data redundancy.
• Enforces user defined rules.
• Ensures data sharing.
• It has automatic and intelligent backup and recovery procedures.
• It has central dictionary to store information.
• Pertaining to data and its manipulation.
• It has different interfaces via which user can manipulate the data.
• Enforces data access authorization.
What is the foreigh key in DBMS explainwith example?
In the context of relational databases, a foreign key is a referential constraint between two tables.[1] The foreign key identifies a column or a set of columns in one (referencing) table that refers to a column or set of columns in another (referenced) table. The columns in the referencing table must be the primary key or other candidate key in the referenced table. A table may have multiple foreign keys, and each foreign key can have a different referenced table. Each foreign key is enforced independently by the database system. Therefore, cascading relationships between tables can be established using foreign keys. Improper foreign key/primary key relationships or not enforcing those relationships are often the source of many database and data modeling problems.
How do you decompress folders on your PC?
It depends how it was compressed Any files I compress I can decompress by simply right-clicking and selecting 'Extract all'
What is Functional dependency and normalization for database?
A functional dependency occurs between two attributes in a database, A and B, if there exists a relationship such that for each value of A there is only one corresponding value of B (A -> B). This can be extended to a functional dependency where A may be a set of tuples (x, y, z) that correspond to a single value B ([x, y, z] -> B). In simple mathematical terms the functional dependency must pass the vertical line test for proper functions. Normalization of a relational database means that the relations (tables) in the database conform to a set of rules for a certain normal form (First - Sixth Normal Form [1-6NF] and/or Boyce-Codd Normal Form [BCNF]). The higher the normal form of a table the less vulnerable it is to data inconsistency and data anomalies formed during updates, inserts, and deletes. Normalization often reduces data redundancy in a database which reduces data inconsistency and anomaly risks. Normalizing a database requires analysis of the closure of the set of functional dependencies to ensure that the set complies with the rules for the given normal form. If the table does not comply with the rules then the table is split following specific procedures to achieve the desired normal form. Every table in a database has a normal form and to make a statement that a database is in a certain normal form (ex. 3NF) means that every table complies with the rules for 3NF.
What a tuple in a relational model?
A row of a table in relational model is known as tuple - is the easy answer. A tuple is a collection of elements that relate to one another : T = R(e1, e2, ... , en). One can view a collection of similar relations, R, as a table, where the elements of same category are projected underneath one another, and ordered as is suited for the table view. When implementing a relational database, the tuples can be spread all over in a way that suits those that make the storage system, and enables fast retrieval and manipulation of them. So, unless you specify the sorting - "Collating Sequence" of the table, you can expect a new ordering every time you view the table. The elements in the relations are bound together in the same way as rows in a table - but some relations may have more elements - "columns" and really belong to other tables - but is "projected" into the view you see as a table.
Because i'm smart and your not i will tell you the answer it helps people find data and it updates it and it can tell you anything and updates anything with in seconds
Security problems in file processing system?
Enforcing Security Constraints in file processing system is very difficult as the application programs are added to the system in an ad-hoc manner.
What kind of program is Microsoft access?
Microsoft Access is a type of database management program. It offers a graphical user interfaces that one can use to create and manage databases.
What is the meaning of the abbreviation 'SQL'?
Structured Query Language, SQL, is used for retrieving and managing data in databases.
What do you understand by a Database-Model?
A database model is a theory or specification describing how a database is structured and used. Several such models have been suggested. Common models include: * Hierarchical model * Network model * Relational model * Entity-relationship * Object-relational model * Object model A data model is not just a way of structuring data: it also defines a set of operations that can be performed on the data. The relational model, for example, defines operations such as select, project, and join. Although these operations may not be explicit in a particular query language, they provide the foundation on which a query language is built.
What are the advantages of numerical filing systems?
- Numerical filing is best for filing large numbers of records.
- It allows the files of patients with the same or similar names to be distinguished more easily.
- The numerical system provides greater security because reference to a patient's name is avoided
8 factor to consider when choosing a database management system?
The hardware needed to run the dbms
the database dbms shouild meet the orgnisations needs for a short period of time
