One-to-many relationships occur when each record in TableA may have many linked records in TableB but each record in TableB may have only one corresponding record in TableA. Learn more about Database Relationships, Foreign Keys, JOINs and E-R Diagrams.
Lunes, Agosto 29, 2011
✿ Foreign key
In the context of relational databases, a foreign key is a referential constraint between two tables.[1]
A foreign key is a field in a relational table that matches a candidate key of another table. The foreign key can be used to cross-reference tables.
The foreign key identifies a column or 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 reference the columns of the primary key or other superkey in the referenced table. The values in one row of the referencing columns must occur in a single row in the referenced table. Thus, a row in the referencing table cannot contain values that don't exist in the referenced table (except potentially NULL). This way references can be made to link information together and it is an essential part ofdatabase normalization. Multiple rows in the referencing table may refer to the same row in the referenced table. Most of the time, it reflects the one (parent table or referenced table) to many (child table, or referencing table) relationship.
The referencing and referenced table may be the same table, i.e. the foreign key refers back to the same table. Such a foreign key is known in SQL:2003 as a self-referencing or recursive foreign key.
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.
✿ Primary Key
The primary key of a relational table uniquely identifies each record in the table. It can either be a normal attribute that is guaranteed to be unique (such as Social Security Number in a table with no more than one record per person) or it can be generated by the DBMS (such as a globally unique identifier, or GUID, in Microsoft SQL Server). Primary keys may consist of a single attribute or multiple attributes in combination.
✿ Ribbon (computing)
In GUI-based application software, a ribbon is an interface where a set of toolbars are placed on tabs in a tab bar. Recent releases of some Microsoft applications have embraced this form with a modular ribbon as their main interface. The Ribbon is a contextual interface that offers functionality based on the context the user is working in. The Ribbon GUI provides the user interface of an application with a large toolbar filled with graphical representations of control elements which are grouped by different functionality. The Ribbon can also contain tabs to expose different sets of control elements eliminating the need for a lot of different icon-based tool bars. Some of these tabs are contextual and appear only when a certain type of object is selected, providing specific tools for items such as tables or images.
http://en.wikipedia.org/wiki/Ribbon_(computing)
http://en.wikipedia.org/wiki/Ribbon_(computing)
✿ Default (computer science)
A default, in computer science, refers to a setting or value automatically assigned to a software application, computer program or device, outside of user intervention. Such settings are also calledpresets, especially for electronic devices. The Oxford English Dictionary dates this usage to the mid-1960s, as a variant of the older meaning of "failure in performance".
Default values are generally intended to make a device (or control) usable "out of the box". A common setting, or at least a usable setting, is typically assigned.
✿How to transfer Physical data to Electronic data
1. Define your business goals and needs. Determine whether you are capturing customer payments, processing applications or archiving internal documents. Figure out if you need to save actual images of the documents for electronic storage, or you simply need to capture the paper-based data into a computer database. Making these determinations will help you decide what data processing system is going to best fit your needs
2. Research enterprise software solutions. Ask for software and vendor references from companies that do similar data capture to what you intend to do. Ask if you can visit work sites doing the sort of paper-to-electronic conversion you intend to do. The best way to choose a system is to see it in action. If you’re only capturing a small volume of data from forms, you can get away with one person typing data into an Excel spreadsheet. But in modern business, this is probably not the case. You will likely need to find a software system, and maybe even new hardware, if document/image capture is part of your plan.
3. Compare the software solutions you have researched, and choose one. Contact the vendor or software distributor to begin the process of purchasing the system and having it installed. The first step, generally known as a “discovery”, is when the vendor travels to your site to determine your exact needs and the best solution for them.
4. Remain engaged with the vendor during the discovery and throughout the installation. Ask lots of questions, and take ownership of the project; encourage any employees who will be performing document capture and data entry activities to do the same.
5. Test the system completely. If there are any bugs or gaps in the solution, it is best to find them while the vendor is on-site. This will make troubleshooting and resolution much quicker.
✿Hierarchical model vs Flat file database model
Hierarchical Model
A hierarchical data model is a data model in which the data is organized into atree-like structure. The structure allows representing information using parent/child relationships: each parent can have many children but each child only has one parent (also known as a 1:many ratio ). All attributes of a specific record are listed under an entity type.In a database, an entity type is the equivalent of a table; each individual record is represented as a row and an attribute as a column. Entity types are related to each other using 1: N mapping, also known as one-to-many relationships. this model is recognized as the first data base model created by IBM in the 1960s. The most recognized and used hierarchical databases areIMS developed by IBM and Windows
Flat File database model
A flat file database is a database that stores data in a plain text file. Each line of the text file holds one record, with fields separated by delimiters, such as commas or tabs. While it uses a simple structure, a flat file database cannot contain multiple tables like a relational database can. Fortunately, most database programs such as Microsoft Access and FileMaker Pro can import flat file databases and use them in a larger relational database.Flat file is also a type of computer file system that stores all data in a single directory. There are no folders or paths used organize the data. While this is a simple way to store files, a flat file system becomes increasingly inefficient as more data is added. The original Macintosh computer used this kind of file system, creatively called the Macintosh File System (MFS). However, it was soon replaced by the more efficient Hierarchical File System (HFS) that was based on a directory structure.
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