Tuesday, July 29, 2008

Geography Markup Language

The Geography Markup Language (GML) is the XML grammar defined by the Open Geospatial Consortium (OGC) to express geographical features. GML serves as a modeling language for geographic systems as well as an open interchange format for geographic transactions on the Internet. Note that the concept of feature in GML is a very general one and includes not only conventional "vector" or discrete objects, but also coverages (see also GMLJP2) and sensor data. The ability to integrate all forms of geographic information is key to the utility of GML.

Monday, July 21, 2008

Navigational database

Navigational databases are characterized by the fact that objects in the database are found primarily by following references from other objects. Traditionally navigational interfaces are procedural, though one could characterize some modern systems like XPath as being simultaneously navigational and declarative.

Navigational access is traditionally associated with the network model and hierarchical model of database interfaces and have evolved into Set-oriented systems . Navigational techniques use "pointers" and "paths" to navigate among data records (also known as "nodes"). This is in contrast to the relational model (implemented in relational databases), which strives to use "declarative" or logic programming techniques in which you ask the system for what you want instead of how to navigate to it.

For example, to give directions to a house, the navigational approach would resemble something like, "Get on highway 25 for 8 miles, turn onto Horse Road, left at the red barn, then stop at the 3rd house down the road".

Monday, July 14, 2008

Database transaction

A database transaction is a unit of work performed against a database management system or similar system that is treated in a coherent and reliable way independent of other transactions. A database transaction, by definition, must be atomic, consistent, isolated and durable. These properties of database transactions are often referred to by the acronym ACID.

Transactions provide an "all-or-nothing" proposition stating that work units performed in a database must be completed in their entirety or take no effect whatever. Further, transactions must be isolated from other transactions, results must conform to existing constraints in the database and transactions that complete successfully must be committed to durable storage.

Tuesday, July 08, 2008

Data extraction

Data extraction is the act or process of retrieving (binary) data out of (usually unstructured or badly structured) data sources for further data processing or data storage (data migration). The import into the intermediate extracting system is thus usually followed by data transformation and possibly the addition of metadata prior to export to another stage in the data workflow.

Usually, the term data extraction is applied when (experimental) data is first imported into a computer from primary sources, like measuring or recording devices. Today's electronic devices will usually present a electrical connector (e.g. USB) through which 'raw data' can be streamed into a personal computer.

Wednesday, July 02, 2008

Electronic signature

The term electronic signature has several meanings. In recent US law, influenced by ABA committee white papers and the National Conference of Commissioners on Uniform State Laws (NCCUSL), electronic signature means "an electronic sound, symbol, or process, attached to or logically associated with a record and executed or adopted by a person with the intent to sign the record." This definition comes from the Uniform Electronic Transactions Act or "UETA" released by NCCUSL in 1999. The U.S. ESign Act of 2000 enacted on a federal level many of the core concepts of UETA. 46 US states, the District of Columbia, and the US Virgin Islands have enacted UETA.

The concept itself is not new. US and other common law contains references to telegraph signatures and faxed signatures, some as far back as the mid-19th century. For that matter, the text of, and comments to, US Federal Rules of Evidence 1001, 1002, and 1003, among others, give good support for the proposition that electronic records and signatures would be admissible in court.