Database Metadata

• Java programs can access databases using Structured Query Language, or SQL. The metadata of databases is the structure of the tables that hold data. Tables are made up of columns, which create fields for each record of data. The columns have a type and a field size associated with them and these details are also stored in the metadata tables. Java includes a command to access the database metadata tables, but the program must first establish a connection with the database. The system that manages Java connections to databases is called JDBC, which stands for Java Database Connectivity. The metadata handling functions are part of a class called DatabaseMetaData. This group includes data types capable of holding metadata read in from the database as well as functions that perform the data fetch.
  
  

Image Metadata

• Image files are encoded by a variety of different encoding standards. The first few lines in the file do not contain the data that represents the image; instead, they contain metadata that describes how the image is stored. This uses a Java library called "imageio." This library includes a Metadata class. The imageio metadata class has a similar structure to the DatabaseMetaData class. The library contains data types that must be used to receive records fetched by the library's functions. The Metadata function reads the image metadata into an XML structure. XML is short for "Extensible Markup Language," which formats data with the use of tags, similar to the Hypertext Markup Language – HTML – used to encode webpages.
  
  

Java Metadata Interface

• Java doesn't only use XML for image metadata. The Java Metadata Interface (JMI) is in XML format. It is an implementation of the Meta Object Facility which was produced by the Object Management Group. MOF is an attempt to create an open standard that, if adopted by all, would establish a neutral method for specifying document and transmission formats expressed in XML. JMI generates format data, which is the metadata of the system. This can be passed on to a receiving third party or even posted on a website with public access. Other MOF-compatible systems can use the metadata to set fields for imported data.
  
  

Annotations

• Java includes a method of commenting in programs referred to as “annotations.” Annotations are classed as metadata. The strict definition of metadata is that it is data that describes data. However, annotations are mainly used to comment on objects in program structure; these objects could be programming code or data objects. An annotation is a label that is added to a declaration of an object. The label is not the name of the object – that forms another part of the object declaration. However the annotations in a program can be used to generate out field labels for screens based on the code.