Database Administration. Database Administration CSCU9Q5. The Data Dictionary. 31Q5/IT31 Database P&A November 7, Overview:

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1 Database Administration CSCU9Q5 Slide 1 Database Administration Overview: Data Dictionary Data Administrator Database Administrator Distributed Databases Slide 2 The Data Dictionary A DBMS must provide facilities to allow users to find out the properties of the stored items (metadata). These facilities may also be used by components of the DBMS itself. Collectively, these facilities are called the Data Dictionary (or the System Catalogue). The Data Dictionary must hold information about the tables, views, forms, queries, and reports stored in the database. for example, it stores information about the name, types, sizes, and constraints that apply to each of the tables in the database It must also store information about the users of the system. For example, it stores the names and details of authorised users including information about which areas of the database are accessible to each user Some of this information is accessible only to the DBA. Slide 3 November 7,

2 The Data Dictionary in Oracle - I In a relational DBMS, the Data Dictionary is often made to look as if it were made up of tables. These tables are views. For example, in Oracle there are many tables with names such as USER_xxx which give information relating to a particular user. For instance, the table USER_CATALOG shows all tables and views owned by the current user. (A synonym for this is CAT) This table has only two columns: name and type Slide 4 The Data Dictionary in Oracle - II Other DD tables have many columns: USER_TABLES (synonym TABS) USER_TAB_COLUMNS (synonym COLS) The columns of these tables are divided into groups: e.g. USER_TAB_COLUMNS has Identification, Definition-Related, and Statistics-Related columns these last are populated only when the table is Analysed Slide 5 The Database Administrator - I Within any organisation using a shared DBMS, we will expect to find a Database Administrator (DBA). At the very minimum (where the users use the DBMS for their own independent purposes), the DBA will be responsible for the orderly running of the program. For instance, an instance of ORACLE runs all the time (even when there are no users logged on to it) and users data is not stored in separate files, but in common data areas and is backed up and journalled (logged) together so at the very least there must be someone who makes sure that all this happens properly. Slide 6 November 7,

3 The Database Administrator - II However, in most organisations (perhaps in all organisations of any significant size), many users will be sharing data and the shared data will be crucial to the core business The data may be divided into different systems - for example the University has Finance Student Records Recruitment and Admissions Vacation letting Estates and Buildings Payroll Personnel Under these circumstances the managerial role of the IS professional is very important indeed (and there will be a team) Slide 7 The DA and the DBA - I There is often a distinction between the roles of the Database Administrator and the Data Administrator, both of which have specific responsibilities that complement each other. The DA has a more strategic and managerial role. The DBA has a more technical role. The DA will be responsible for the Information Strategy of the organisation as a whole (i.e. transcending the various subsystems) and will be concerned with large-scale developments (e.g. moving subsystems between platforms, developing new subsystems, ensuring resilience, developing & maintaining standards, policies & procedures etc.) Slide 8 The DA and the DBA - II The DBA role is concerned more with managing a particular (sub)system on a particular platform The DBA will have roles both during the setting-up of a system, and, later, while it is running. The DBA will with the DA, participate in deciding the information content of the database write the conceptual specification ( conceptual schema ) decide how the data should be stored: use the facilities of the DBMS to provide the mapping from the logical to the physical Slide 9 November 7,

4 The DBA will also The DA and the DBA - III write sub-schemas for user views document the views allocate ownership rights and duties with the DA, adjudicate between different interests use the DBMS management tools to monitor, tune, reorganise, protect, backup, and reload Slide 10 Management tools used by the DBA Any mature DBMS will provide tools to: bulk load data from files in other formats restructure data: for example to distribute data across several sites provide differential access to data in ways that can be configured and restructured maintain dynamic backup and restore facilities to enable rapid recovery of a DBMS whose platform crashes (these facilities may be automatic but configurable by the DBA) give access to data about the DBMS, its contents, its users and its performance (via the Data Dictionary) retune parameters to improve performance (eg, Hints in ORACLE) Slide 11 Distributed Databases Distributed Database A logically interrelated collection of shared data (and a description of this data), physically distributed over a computer network. Could be across two computers in the same room or lots of computers across the world Under the control of more than one CPU Distributed DBMS Software system that permits the management of the distributed database and makes the distribution transparent to users. Slide 12 November 7,

5 Slide 13 Key Concepts Collection of logically-related shared data. Data split into fragments. Fragments may be replicated. Fragments/replicas allocated to sites. Sites linked by a communications network. Data at each site is under control of a DBMS. DBMSs handle local applications autonomously. Each DBMS participates in at least one global application. Slide 14 Advantages of DDBMS Reflects organizational structure database fragments are located in the departments they relate to. Local autonomy a department can control the data about them (as they are the ones familiar with it.) Improved availability a fault in one database system will only affect one fragment, instead of the entire database. Improved performance data is located near the site of greatest demand, and the database systems themselves are parallelized, allowing load on the databases to be balanced among servers. (A high load on one module of the database won't affect other modules of the database in a distributed database.) Economics it costs less to create a network of smaller computers with the power of a single large computer. Modularity systems can be modified, added and removed from the distributed database without affecting other modules (systems). Slide 15 November 7,

6 Disadvantages of DDBMS Complexity extra work must be done by the DBAs to ensure that the distributed nature of the system is transparent. Extra work must also be done to maintain multiple disparate systems, instead of one big one. Extra database design work must also be done to account for the disconnected nature of the database for example, joins become prohibitively expensive when performed across multiple systems. Economics increased complexity and a more extensive infrastructure means extra labour costs. Security remote database fragments must be secured, and they are not centralized so the remote sites must be secured as well. The infrastructure must also be secured (e.g., by encrypting the network links between remote sites). Difficult to maintain integrity in a distributed database, enforcing integrity over a network may require too much of the network's resources to be feasible. Inexperience distributed databases are difficult to work with, and as a young field there is not much readily available experience on proper practice. Slide 16 DDBMS DDBMS is a Distributed Database Management System with Extended communication services. Extended Data Dictionary. Distributed query processing. Extended concurrency control. Extended recovery services. Plus all the functionality you would expect from a centralized DBMS Slide 17 Two Types of DDB Homogeneous DDBMS All sites use same DBMS product. Much easier to design and manage. Approach provides incremental growth and allows increased performance. Heterogeneous DDBMS Sites may run different DBMS products, with possibly different underlying data models. Occurs when sites have implemented their own databases and integration is considered later. Translations required to allow for: Different hardware. Different DBMS products. Different hardware and different DBMS products. Typical solution is to use gateways. Slide 18 November 7,

7 Which Type and Why? Homogeneous DDBMS Databases that are homogeneous were probably designed to be distributed from the start The designers had the luxury of being able to choose a common DBMS Foreign keys allow tables in one database to be linked to tables in another The physical distribution is probably for security and service protection. Far fewer problems to solve when building and maintaining such a database This type of design is known as top down. Slide 19 Which Type and Why? Heterogeneous DDBMS The different databases probably already exist and are in use by different users It becomes desirable to join them into one apparently single database, without simply throwing them all away and starting again They could each have a different DBMS They will be more than one DD, DA and DBA They may not be an easy way of matching fields from one to equivalent fields in another Joining such databases is known as a Bottom Up join Slide 20 Example A bank has a database of current account users, another with mortgage holders and a third with customer relations data. If the marketing department want to see what services a customer has bought, and when they last wrote to them, they have to look the customer up in three different databases. The databases can become out of synch, for example if a person moves house and tells the bank once. The mortgage account DB might get updated, but the current account DB might not, and the customer relations DB almost certainly will not. By joining the databases, the bank can have a single customer view, which is something they like. Slide 21 November 7,

8 Joining a DDBMS Bottom Up The job of the DDBMS is to sit above the several separate databases and provide the user with a single view as if there were really only one database It does not integrate the databases into one new single database. They stay where they are. One method of achieving this is to use a gateway, which translates from one DBMS to another There are also attempts being made to develop open specifications that will allow one DBMS to communicate with another without the need for a gateway. A much more difficult problem is joining the data from more than one DB, for example, the current account DB has William Smith, but marketing communicate with Bill Smith. Slide 22 Joining a DDBMS Bottom Up Bottom up joins have many difficulties because the databases were not designed to be joined. Each will have its own DBA, so there needs to be human integration too The purpose for which a DB was designed may not match the reasons that it is needed when it has been joined E.g. city council social services Slide 23 Partitioning Schemes Any part of a distributed database is called a fragment For homogeneous DDBs, the most common forms of partitioning are horizontal and vertical: Horizontal partitioning is where different full records from a table are stored in different locations. Example: Imagine the car dealership chain, Arnold Clark. They will use a dealer management system such as Kerridge. The tables in each dealership will have the same structure (homogeneous) but different customers will appear in each. If head office want to write to every customer, regardless of where they bought the car, they need the DDBMS to be able to respond to a query that generates every customer across all the databases in each dealership. Slide 24 November 7,

9 Partitioning Schemes Any part of a distributed database is called a fragment For homogeneous DDBs, the most common forms of partitioning are horizontal and vertical: Vertical partitioning is where different attributes are stored in different locations. Example: I probably appear on a few databases in the university: payroll, car parking, timetabling, sports centre If the university wanted to be able to make a single query and see everything they have about me, it would be from a number of different databases. Chances are, they couldn t do it because the DBs are not under a DDBMS. Slide 25 November 7,

Distributed DBMS. Concepts. Concepts. Distributed DBMS. Concepts. Concepts 9/8/2014

Distributed DBMS. Concepts. Concepts. Distributed DBMS. Concepts. Concepts 9/8/2014 Distributed DBMS Advantages and disadvantages of distributed databases. Functions of DDBMS. Distributed database design. Distributed Database A logically interrelated collection of shared data (and a description